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infra-

  1. a prefix meaning “below,” used, with second elements of any origin, in the formation of compound words: infrasonic; infrared.
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Origin of infra-

< Latin, representing infrā, adv. or preposition
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
British Dictionary definitions for infra-

infra-

prefix
  1. below; beneath; afterinfrasonic; infralapsarian
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Word Origin for infra-

from Latin infrā
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 infra-

word-forming element from Latin infra (adv., prep.) "below, underneath, beneath; later than, smaller, inferior to," from PIE *ndher "under" (cf. Sanskrit adnah "below," Old English under "under, among;" see under). Opposed to super-. Its use as a prefix was rare in Latin.

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Online Etymology Dictionary, © 2010 Douglas Harper
infra- in Medicine

infra-

pref.
  1. Inferior to, below, or beneath:infrasonic.
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The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.