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[yoo-nuh-lat-er-uh l] /ˌyu nəˈlæt ər əl/
relating to, occurring on, or involving one side only:
unilateral development; a unilateral approach.
undertaken or done by or on behalf of one side, party, or faction only; not mutual:
a unilateral decision; unilateral disarmament.
having only one side or surface; without a reverse side or inside, as a Möbius strip.
  1. pertaining to a contract that can be formed only when the party to whom an offer is made renders the performance for which the offeror bargains.
  2. pertaining to a contract in which obligation rests on only one party, as a binding promise to make a gift.
Botany. having all the parts disposed on one side of an axis, as an inflorescence.
through forebears of one sex only, as through either the mother's or father's line.
Compare bilateral (def 5).
Phonetics. (of an l -sound) characterized by passage of air on only one side of the tongue.
Origin of unilateral
From the New Latin word ūnilaterālis, dating back to 1795-1805. See uni-, lateral
Related forms
unilaterality, noun
unilaterally, adverb Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2018.
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British Dictionary definitions for unilateral


of, having, affecting, or occurring on only one side
involving or performed by only one party of several: unilateral disarmament
(law) (of contracts, obligations, etc) made by, affecting, or binding one party only and not involving the other party in reciprocal obligations
(botany) having or designating parts situated or turned to one side of an axis
(sociol) relating to or tracing the line of descent through ancestors of one sex only Compare bilateral (sense 5)
(phonetics) denoting an (l) sound produced on one side of the tongue only
Derived Forms
unilateralism, unilaterality, noun
unilaterally, adverb
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for unilateral

1802, from Modern Latin unilateralis, from unum, neuter of unus "one" (see one) + latus (genitive lateralis) "side" (see oblate (n.)). Jeremy Bentham (1748-1832) may have been the first to use it in the legal sense of "made or entered into by one party." Unilateral disarmament is recorded from 1929.

It is useless for the sheep to pass resolutions in favor of vegetarianism, while the wolf remains of a different opinion. [William Ralph Inge, "Outspoken Essays," 1919]

Online Etymology Dictionary, © 2010 Douglas Harper
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unilateral in Medicine

unilateral u·ni·lat·er·al (yōō'nə-lāt'ər-əl)
On, having, or confined to only one side.

u'ni·lat'er·al·ly adv.
The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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