twin

Etymology 1

PIE word *dwóh₁ From Middle English twinne, twynne, from Old English ġetwin, ġetwinn (“twin, multiple”, noun) and twinn (“twin, two-fold, double, two by two”, adjective), from Proto-Germanic *twinjaz, *twinaz (“two each”), from Proto-Indo-European *dwino- (“twin”), from *dwóh₁ (“two”). Cognate with Scots twyn (“twin”), Dutch tweeling (“twin”), German Zwilling (“twin”), Swedish tvilling (“twin”), Faroese tvinnur (“a double set”), Icelandic tvenna (“duo, pair”), Lithuanian dvynys (“twin”), Russian двойня (dvojnja, “twin”).

noun

1. Either of two people (or, less commonly, animals) who shared the same uterus at the same time; one who was born at the same birth as a sibling.
2. Either of two similar or closely related objects, entities etc.
3. A room in a hotel, guesthouse, etc. with two beds; a twin room.
4. (US) A twin size mattress or a bed designed for such a mattress.
5. (aviation) A two-engine aircraft.
6. (crystallography) A twin crystal.

verb

1. (transitive, obsolete outside Scotland) To separate, divide.
2. (intransitive, obsolete outside Scotland) To split, part; to go away, depart.
3. (usually in the passive) To join, unite; to form links between (now especially of two places in different countries); to pair with.
   Reading, the English town, is twinned with Clonmel in Ireland.
   Coventry twinned with Dresden as an act of peace and reconciliation, both cities having been heavily bombed during the war.
   Yet, Manet heightens its effect by performing the clever ocular trick of practically twinning her with her pictorial counterpart, Madame Lejosne. 2006, Aruna D'Souza, Tom McDonough, Tom Mc Donough, The Invisible Flâneuse?: Gender, Public Space, and Visual Culture in Nineteenth-century Paris, Manchester University Press, page 60
4. (intransitive) To give birth to twins.
   “I’ve run to tell ye,” said the junior shepherd, supporting his exhausted youthful frame against the doorpost, “that you must come directly. Two more ewes have twinned — that’s what’s the matter, Shepherd Oak.” 1874, Thomas Hardy, Far from the Madding Crowd
   Twinning today is abnormal in all higher primates, and possibly adaptive only in the one species with an obstetrical technology that permits a high rate of survival of twins. 1992, George Christopher Williams, Natural Selection: Domains, Levels, and Challenges, Oxford University Press on Demand, page 79
5. (transitive) To be, or be like, a twin to (someone else); to match in some way.
   The invert child and her innocent child are together lost children, twinning each other despite their distinctions. 2009, Kathryn Bond Stockton, The Queer Child, or Growing Sideways in the Twentieth Century, Duke University Press, page 111
   I was awake to the horror of our twinning each other in paralysis, and feared that we would soon talk only about the daily, intimate care serious paralysis demands […] 2017, Christina Crosby, A Body, Undone: Living On After Great Pain, NYU Press, page 111
6. (intransitive) To be, or be like, a pair of twins (for example, to dress identically); to be paired or suited.
   “I see you got us twinning today.” Byrd kissed Lay quickly. “I wanted you to dress like me today,” he admitted. 2018, Vivian Blue, Your Heart Is Mine: A Criminal Romance, Sullivan Group Publishing
   “We're totally twinning today!” said Zoey. “You sure are,” said Chef Piper. “I whipped up a special dessert for tonight.” 2019, Lisa Mullarkey, Paisley, ABDO, page 17

Etymology 2

From Middle English *twin, *twyn, from Old English twin, twinn (“twin; double”, adjective), from Proto-Germanic *twīhnaz (“occurring in a pair; twofold; double”), from Proto-Indo-European *dwóh₁ (“two”). Cognate with Icelandic tvennur (“double”), Gothic 𐍄𐍅𐌴𐌹𐌷𐌽𐌰𐌹 (tweihnai, “two each”).

adj

1. Double; dual; occurring as a matching pair.
   twin beds, twin socks
2. Forming a pair of twins.
   the twin boys