parenthesis

Etymology

Learned borrowing from Late Latin parenthesis (“addition of a letter to a syllable in a word”), itself borrowed from Ancient Greek παρένθεσις (parénthesis).

noun

1. A clause, phrase or word which is inserted (usually for explanation or amplification) into a passage which is already grammatically complete, and usually marked off with brackets, commas or dashes.
2. Either of a pair of brackets, especially round brackets, ( and ) (used to enclose parenthetical material in a text).
   There be five manner of points and divisions most used among cunning men; the which if they be well used, make the sentence very light and easy to be understood, both to the reader and hearer: and they be these, virgil,—come,—parenthesis,—plain point,—interrogative[…] it is a slender stroke leaning forward, betokening a little short rest, without any perfectness yet of sentence. 1824, John Johnson, Typographia, Or the Printer's Instructor, London: Longman, Hurst, Rees, Orme, Brown and Green
   Whoever introduced the several points, it seems that a full-point, a point called come, answering to our colon-point, a point called virgil answering to our comma-point, the parenthesis-points and interrogative-point, were used at the close of the fourteenth, or beginning of the fifteenth century. 1842, F. Francillon, An Essay on Punctuation, page 9
   [T]he present research also made an effort to approach a greater accuracy in presenting the original sources of borrowed words. This was achieved by presenting etymons from Hindustani in the Devanagari script followed by a transliteration in the Roman alphabet in parentheses. 2018, James Lambert, “Anglo-Indian slang in dictionaries on historical principles”, in World Englishes, volume 37, page 255
3. (rhetoric) A digression; the use of such digressions.
   Ryan Bingham (George Clooney): I thought I was a part of your life. Alex Goran (Vera Farmiga): I thought we signed up for the same thing[…] I thought our relationship was perfectly clear. You are an escape. You're a break from our normal lives. You're a parenthesis. Ryan Bingham (George Clooney): I'm a parenthesis? 2009, Up in the Air
4. (mathematics, logic) Such brackets as used to clarify expressions by grouping those terms affected by a common operator, or to enclose the components of a vector or the elements of a matrix.