Origins
Few words reveal their meaning as transparently as 'infant.' Strip away the centuries and the word announces exactly what it names: a creature that cannot yet speak.βββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ The Latin 'infΔns' is a pure negation β 'in-' (not) plus 'fΔns' (speaking) β and it marks the boundary that every human being crosses in childhood: the passage from silence into language.
The word entered English in the late fourteenth century through Old French 'enfant' (child, young person), which itself descends from Latin 'infΔns' (genitive 'infantis'), meaning 'not speaking, speechless,' and by extension 'a young child.' The French form 'enfant' broadened its meaning to cover children of all ages, while English 'infant' narrowed back toward the Latin sense of a very young child, typically one not yet able to speak or walk.
Latin 'fΔrΔ«' (to speak, to say, to utter) comes from PIE *bΚ°ehβ- (to speak), a root that produced a remarkable cluster of English words. 'Fable' comes from Latin 'fΔbula' (a story, a tale β literally, a thing spoken). 'Fame' comes from Latin 'fΔma' (report, rumor, reputation β what is spoken about someone). 'Fate' comes from Latin 'fΔtum' (that which has been spoken β a prophetic utterance, a decree of the gods). 'Fatal' shares this origin: what fate has decreed. 'Affable' means literally 'easy to speak to.' 'Ineffable' means 'unspeakable, too great for words.' 'Confess' comes from Latin 'confitΔrΔ«' (to acknowledge, to speak together β from 'con-' + 'fatΔrΔ«,' an intensive form of 'fΔrΔ«'). 'Profess' (to declare publicly), 'preface' (something spoken before), and 'prophet' (one who speaks forth β though this last word has a Greek route, from 'pro-' + 'phΔnai,' to speak) all belong to this web of speech-words.
Proto-Indo-European Roots
The Greek cognate of 'fΔrΔ«' is 'phΔnai' (to speak) and its derivatives 'phΔmΔ' (speech, utterance) and 'phΕnΔ' (voice, sound). From these come 'phone,' 'phonetic,' 'euphemism' (speaking well, using pleasant words), 'blasphemy' (harmful speech), 'aphasia' (speechlessness), and 'dysphemism.' The PIE root connects Latin 'speech about things' with Greek 'voice and sound,' different facets of the same human capacity.
The legal sense of 'infant' is older and broader than the everyday one. In English common law, an 'infant' was any person under the age of majority β originally twenty-one. This legal usage persisted well into the twentieth century, so that a twenty-year-old could be called an 'infant' in court documents. The underlying logic was the same: an infant in law was someone not yet empowered to speak for themselves in legal matters, unable to enter contracts or give consent.
The connection between 'infant' and 'infantry' is one of etymology's great surprises. Italian 'infante' meant both 'child' and 'young servant,' and by extension 'foot soldier' β the lowest-ranking fighters who served on foot rather than on horseback. 'Infanteria' (foot soldiers collectively) entered French as 'infanterie' and English as 'infantry' by the sixteenth century. The knight rode; the infant walked. The social hierarchy between mounted nobility and their young attendants is preserved in the military terminology to this day.