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late 14c., "child during earliest period of life" (sometimes extended to age 7 and sometimes including a fetus), from Latin infantem (nominative infans) "young child, babe in arms," noun use of adjective meaning "not able to speak," from in- "not, opposite of" (see in- (1)) + fans, present participle of fari "speak" (see fame (n.)). As an adjective, 1580s, from the noun.
infant in·fant (ĭn'fənt)
A child in the earliest period of life, especially before he or she can walk.