open

Etymology 1

From Middle English open, from Old English open (“open”), from Proto-West Germanic *opan, from Proto-Germanic *upanaz (“open”), from Proto-Indo-European *upo (“up from under, over”). Cognate with Scots apen (“open”), Saterland Frisian eepen (“open”), West Frisian iepen (“open”), Dutch open (“open”), Low German open, apen (“open”), German offen (“open”), Danish åben (“open”), Swedish öppen (“open”), Norwegian Bokmål åpen (“open”), Norwegian Nynorsk open (“open”), Icelandic opinn (“open”). Compare also Latin supinus (“on one's back, supine”), Albanian hap (“to open”). Related to up.

adj

1. (usually not comparable) Not closed.
   1. Able to be accessed (physically).
   2. Able to have something pass through or along it.
      Turn left after the second open door.
   3. (of a body part) Not covered; showing what is inside.
      It was as if his body had gone to sleep standing up and with his eyes open.
2. Not physically drawn together, closed, folded or contracted; extended.
   an open hand; an open flower
3. (not comparable) Actively conducting or prepared to conduct business.
   Banks are not open on bank holidays.
   Since the launch early last year of […] two Silicon Valley start-ups offering free education through MOOCs, massive open online courses, the ivory towers of academia have been shaken to their foundations. University brands built in some cases over centuries have been forced to contemplate the possibility that information technology will rapidly make their existing business model obsolete. 2013-07-20, “The attack of the MOOCs”, in The Economist, volume 408, number 8845
4. (comparable) Receptive.
   I am open to new ideas.
   When the top sheet, blanket, and bedspread of a closed bed are turned back, or fanfolded, the closed bed becomes an open bed, or a bed ready to receive a patient or resident. 2005, Pamela J. Carter, Susan Lewsen, Lippincott's Textbook for Nursing Assistants, page 277
   A U.K. survey found attitudes toward public transit had been set back by two decades, with only 43% of drivers open to using their car less, even if public transport improves. April 2 2021, Ciara Nugent, “Can Public Transit Survive the Pandemic? London's New Transport Commissioner Wants You to Believe It Can”, in Time
5. (not comparable) Public
   He published an open letter to the governor on a full page of the New York Times.
   Due to severe and pervasive discrimination, people dared not be open about their homosexuality, and because no one would be open, social prejudice and discrimination became even stronger. 2001, Xiaopei He, “Chinese Queer (Tongzhi) Women Organizing in the 1990s”, in Ping-Chun Hsiung, Maria Jaschok, Cecilia Milwertz, Red Chan, editors, Chinese Women Organizing: Cadres, Feminists, Muslims, Queers, Berg, →LCCN, →OCLC, page 41
6. (not comparable) With open access, of open science, or both.
   hopes for all aspects of the project being open rather than paywalled
7. (not comparable) Candid, ingenuous, not subtle in character.
   The man is an open book.
   1731-1735, Alexander Pope, Moral Essays with aspect open, shall erect his head
8. (now regional) Mild (of the weather); free from frost or snow.
   He desires me to tell you that the present open weather induces him to accept Mr Vernon's invitation to prolong his stay in Sussex that they may have some hunting together. c. 1794, Jane Austen, Lady Susan
9. (mathematics, logic, of a formula) Having a free variable.
10. (mathematics, topology, of a set) Which is part of a predefined collection of subsets of X, that defines a topological space on X.
11. (graph theory, of a walk) Whose first and last vertices are different.
12. (computing, not comparable, of a file, document, etc.) In current use; connected to as a resource.
    I couldn't save my changes because another user had the same file open.
13. (engineering, gas and liquid flow, of valve or damper) To be in a position allowing fluid to flow.
14. (electricity, of a switch or circuit breaker) To be in a position preventing electricity from flowing.
15. (business) Not fulfilled.
    I've got open orders for as many containers of red durum as you can get me.
16. Not settled or adjusted; not decided or determined; not closed or withdrawn from consideration.
    an open question
    to keep an offer or opportunity open
    your account will remain open until we receive final settlement.
17. (music, stringed instruments) Of a note, played without pressing the string against the fingerboard.
18. (music) Of a note, played without closing any finger-hole, key or valve.
19. Not of a quality to prevent communication, as by closing waterways, blocking roads, etc.; hence, not frosty or inclement; mild; used of the weather or the climate.
    an open winter
20. (law, of correspondence) Written or sent with the intention that it may made public or referred to at any trial, rather than by way of confidential private negotiation for a settlement.
    You will observe that this is an open letter and we reserve the right to mention it to the judge should the matter come to trial.
21. (phonetics) Uttered with a relatively wide opening of the articulating organs; said of vowels.
    "Supposing somebody sees you, with all those flowers too? Supposing somebody writes him a letter? Ooooh!" (a pure round open Tamil O.) 1959, Anthony Burgess, Beds in the East (The Malayan Trilogy), published 1972, page 421
22. (phonetics) Uttered, as a consonant, with the oral passage simply narrowed without closure.
23. (phonetics, of a syllable) That ends in a vowel; not having a coda.
24. (computing, education) Made public, usable with a free licence and without proprietary components.
25. (medicine) Resulting from an incision, puncture or any other process by which the skin no longer protects an internal part of the body.
26. (computing, used before "code") Source code of a computer program that is not within the text of a macro being generated.
27. (of a multi-word compound) Having component words separated by spaces, as opposed to being joined together or hyphenated; for example, time slot as opposed to timeslot or time-slot.

Etymology 2

From Middle English openen, from Old English openian (“to open”), from Proto-Germanic *upanōną (“to raise; lift; open”), from Proto-Germanic *upanaz (“open”, adjective). Cognate with Saterland Frisian eepenje (“to open”), West Frisian iepenje (“to open”), Dutch openen (“to open”), German öffnen (“to open”), Danish åbne (“to open”), Swedish öppna (“to open”), Norwegian Bokmål åpne (“to open”), Norwegian Nynorsk and Icelandic opna (“to open”). Related to English up.

verb

1. (transitive) To make something accessible or allow for passage by moving from a shut position.
   Turn the doorknob to open the door.
   I made a speaking trumpet of my hands and commenced to whoop “Ahoy!” and “Hello!” at the top of my lungs. […] The Colonel woke up, and, after asking what in brimstone was the matter, opened his mouth and roared “Hi!” and “Hello!” like the bull of Bashan. 1913, Joseph C. Lincoln, chapter 7, in Mr. Pratt's Patients
   ‘No. I only opened the door a foot and put my head in. The street lamps shine into that room. I could see him. He was all right. Sleeping like a great grampus. Poor, poor chap.’ 1963, Margery Allingham, chapter 20, in The China Governess
2. (transitive) To make (an open space, etc.) by clearing away an obstacle or obstacles, in order to allow for passage, access, or visibility.
   He opened a path through the undergrowth.
   He had kept on recording everything then, when he had been sure he was going to die, and he went on recording everything now, when he was suddenly consumed with hate for the boy in his arms and overwhelmed by a desire to put something—his motorcycle key would do nicely — into the interfering little prayboy’s throat and open him like a can of beer. 1996, Stephen King, Desperation
3. (transitive, intransitive, engineering, gas and liquid flow, of valve or damper) To move to a position allowing fluid to flow.
4. (transitive, intransitive, electricity, of a switch, fuse or circuit breaker) To move to a position preventing electricity from flowing.
5. (Manglish, Philippines) To turn on; to switch on.
   Open your webcam. ― Turn on your webcam.
   Open the fan please. ― Please switch on the fan.
   Open the lights please. ― Please turn on the lights.
6. (transitive) To bring up, broach.
   I don't want to open that subject.
7. (transitive) To enter upon, begin.
   to open a discussion
   to open fire upon an enemy
   to open trade, or correspondence
   to open a case in court, or a meeting
8. (transitive) To spread; to expand into an open or loose position.
   to open a closed fist
   to open matted cotton by separating the fibres
   to open a map, book, or scroll
9. (transitive) To make accessible to customers or clients.
   I will open the shop an hour early tomorrow.
   Suiping was opened as a main station in 1912 when Rev. H. M. Nesse arrived to take charge of the mission work. 1934, White Unto Harvest in China: A Survey of the Lutheran United Mission, the China Mission of the N.L.C.A., 1890-1934, →OCLC, page 76
10. (transitive) To start (a campaign).
    Vermont will open elk hunting season next week.
11. (intransitive) To become open.
    The door opened all by itself.
    I stumbled along through the young pines and huckleberry bushes. Pretty soon I struck into a sort of path that, I cal'lated, might lead to the road I was hunting for. It twisted and turned, and, the first thing I knew, made a sudden bend around a bunch of bayberry scrub and opened out into a big clear space like a lawn. 1913, Joseph C. Lincoln, chapter 1, in Mr. Pratt's Patients
12. (intransitive) To begin conducting business.
    The shop opens at 9:00.
13. (intransitive, cricket) To begin a side's innings as one of the first two batsmen.
14. (intransitive, poker) To bet before any other player has in a particular betting round in a game of poker.
    After the first two players fold, Julie opens for $5.
15. (transitive, intransitive, poker) To reveal one's hand.
    Jeff opens his hand revealing a straight flush.
16. (computing, transitive, intransitive) To connect to a resource (a file, document, etc.) for viewing or editing.
17. (transitive, nursing) To make (a bed) ready for a patient by folding back the bedcovers.
    Follow agency policy, or open the bed by folding the top linens back. 2013, Susan C. deWit, Patricia A. Williams, Fundamental Concepts and Skills for Nursing, page 318
18. (obsolete) To disclose; to reveal; to interpret; to explain.
    The king opened himself to some of his council, that he was sorry for the earl's death. 1622, Francis Bacon, The History of the Reign of King Henry the Seventh

Etymology 3

From Middle English open (“an aperture or opening”), from the verb (see Etymology 2 above). In the sports sense, however, a shortening of “open competition”.

noun

1. (with the) Open or unobstructed space; an exposed location.
   I can't believe you left the lawnmower out in the open when you knew it was going to rain this afternoon!
   Wary of hunters, the fleeing deer kept well out of the open, dodging instead from thicket to thicket.
2. (with the) Public knowledge or scrutiny; full view.
   We have got to bring this company's corrupt business practices into the open.
3. (electronics) A defect in an electrical circuit preventing current from flowing.
   The electrician found the open in the circuit after a few minutes of testing.
4. A sports event in which anybody can compete.
   the Australian Open
5. The act of something being opened, such as an e-mail message.
   The total number of opens from original, or unique, subscribers. 2016, Ian Dodson, The Art of Digital Marketing, page 144