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anti-

  1. a prefix meaning “against,” “opposite of,” “antiparticle of,” used in the formation of compound words (anticline); used freely in combination with elements of any origin (antibody; antifreeze; antiknock; antilepton).
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Also before a vowel, ant-.

Origin of anti-

Middle English < Latin < Greek, prefixal use of antí; akin to Sanskrit ánti opposite, Latin ante, Middle Dutch ende (> Dutch en and), English an- in answer. Cf. ante-, and
Can be confusedante ante- anti- auntie
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

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British Dictionary definitions for anti-

anti-

prefix
  1. against; opposinganticlerical; antisocial
  2. opposite toanticlimax; antimere
  3. rival; falseantipope
  4. counteracting, inhibiting, or neutralizingantifreeze; antihistamine
  5. designating the antiparticle of the particle specifiedantineutron
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Word Origin for anti-

from Greek anti
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

Word Origin and History for anti-

word-forming element meaning "against, opposed to, opposite of, instead," from Old French anti- and directly from Latin anti-, from Greek anti "against, opposite, instead of," also used as a prefix, from PIE *anti "against," also "in front of" (see ante). It appears in some words in Middle English but was not commonly used in word formations until modern times.

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Online Etymology Dictionary, © 2010 Douglas Harper

anti- in Medicine

anti-

pref.
  1. Opposite:antimere.
  2. Opposing; against:antisocial.
  3. Counteracting; neutralizing:antibody.
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The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.

anti- in Science

anti-

  1. A prefix whose basic meaning is “against.” It is used to form adjectives that mean “counteracting” (such as antiseptic, preventing infection). It is also used to form nouns referring to substances that counteract other substances (such as antihistamine, a substance counteracting histamine), and nouns meaning “something that displays opposite, reverse, or inverse characteristics of something else” (such as anticyclone, a storm that circulates in the opposite direction from a cyclone). Before a vowel it becomes ant-, as in antacid.
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The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.