late 14c.,infant,infaunt, "a child," also especially "child during earliest period of life, a newborn" (sometimes meaning a fetus), from Latininfantem (nominativeinfans) "young child, babe in arms," noun use of adjective meaning "not able to speak," fromin- "not, opposite of" (seein- (1)) +fans, present participle offari "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 Latininfans to include older children, hence Frenchenfant "child," Italianfanciullo,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 bybairn andchild) also are sense extensions of words that originally must have meant "newborn."

1837, frominfantry +man (n.).