late 14c., infant, infaunt, "a child," also especially "child during earliest period of life, a newborn" (sometimes meaning 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 "to speak," from PIE root *bha- (2) "to speak, tell, say." As an adjective in English, 1580s, from the noun.
The Romans extended the sense of Latin infans to include older children, hence French enfant "child," Italian fanciullo, fanciulla. In English the word formerly also had the wider sense of "child" (commonly reckoned as up to age 7). The common Germanic words for "child" (represented in English by bairn and child) also are sense extensions of words that originally must have meant "newborn."
mid-15c., "ripe;" 1520s, "existing or done before the proper or usual time, arriving too early at maturity," from Latin praematurus "early ripe" (as fruit), "too early, untimely," from prae "before" (see pre-) + maturus "ripe, timely" (see mature (v.)). Related: Prematurely; prematurity; prematuration.
Premature ejaculation is attested from 1848; the Latin euphemism ejaculatio praecox dates to 1891 in English but was used earlier in German and appears to have been, at first at least, the psychologist's term for it.
mid-15c., "pertaining to infants," from Late Latin infantilis "pertaining to an infant," from infans "young child" (see infant). Sense of "infant-like" is from 1772.
"premature growth, ripeness, or development," 1630s, from French précocité (17c.), from précoce "precocious," from Latin praecocem (nom. praecox) "maturing early;" see precocious.
"daughter of a king of Spain or Portugal," c. 1600, from Spanish and Portuguese infanta, fem. of infante "a youth; a prince of royal blood," from Latin infantem (see infant).