How are the words infant and infantry connected? Pretty whimsically, it turns out. In French, the word for infant was infante, which originally meant "youth" under a connection of inexperience. Both of these words trace to Latin noun infans, with the same meaning as infant today. This, however, comes from two other parts: the prefix in-, implying an opposite (and hailing from Proto-Indo-European n, meaning "not"), and the root fans, which meant "speaking". An infant, therefore, is one who does not speak (and, by extension, so is the infantry). Fans comes from the Proto-Italic reconstruction faor, from Proto-Indo-European bha, still meaning "to speak". In English literature today, the word infant is used about four times more often than infantry, although application of both has decreased over time.
Adam Aleksic has been described as the internet's sixth most famous etymologist. He loves writing about himself in the third person, he's a freshman at Harvard University, and he has disturbing interests in linguistics, vexillology, geography, board games, limericks, and law.
The Etymology Nerd