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infantile

[in-fuh n-tahyl, -til]
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adjective
  1. characteristic of or befitting an infant; babyish; childish: infantile behavior.
  2. of or relating to infants or infancy: infantile diseases.
  3. Physical Geography. youthful(def 5).
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Origin of infantile

From the Latin word infantīlis, dating back to 1690–1700. See infant, -ile
Related formsin·fan·til·i·ty [in-fuh n-til-i-tee] /ˌɪn fənˈtɪl ɪ ti/, noun

Synonyms

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1. puerile, immature, weak.

Synonym study

1. See childish.

Antonyms

1. adult, mature.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

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British Dictionary definitions for infantile

infantile

adjective
  1. like a child in action or behaviour; childishly immature; puerile
  2. of, relating to, or characteristic of infants or infancy
  3. in an early stage of development
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Derived Formsinfantility (ˌɪnfənˈtɪlɪtɪ), noun
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 infantile

adj.

mid-15c., "pertaining to infants," from Latin infantilis "pertaining to an infant," from infans (see infant). Sense of "infant-like" is from 1772.

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Online Etymology Dictionary, © 2010 Douglas Harper
infantile in Medicine

infantile

(ĭn′fən-tīl′, -tĭl)
adj.
  1. Of or relating to infants or infancy.
  2. Displaying or suggesting a lack of maturity; extremely childish.
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The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.