Origins
The prefix 'anti-' is one of the most recognizable and productive word-forming elements in the English language. It descends from Greek 'antí' (ἀντί), a preposition and prefix meaning 'against,' 'opposite,' 'in return,' or 'in place of.' The Greek word traces to PIE *h₂enti, meaning 'front,' 'forehead,' or 'before' — a spatial concept that evolved into opposition, the idea of standing face-to-face against something.
In Greek, 'antí' had a richer semantic range than its English descendant typically carries. It could mean 'in exchange for' or 'in place of' (the sense preserved in 'antiphon,' a response sung in alternation), 'corresponding to' or 'matching,' as well as the more familiar 'against' and 'opposite.' Homer used 'antí' frequently in the Iliad to describe warriors standing face-to-face in combat — the original spatial metaphor of frontal opposition.
The prefix entered English through multiple channels. The earliest English words containing 'anti-' arrived through Latin and Old French translations of biblical and theological texts. 'Antichrist' — from Greek 'antíkhristos' (ἀντίχριστος, opponent of Christ) — appears in English by the fourteenth century. 'Antidote' arrived in the fifteenth century from Greek 'antídoton' (ἀντίδοτον, given against), a remedy 'given against' a poison. 'Antipathy' followed from Greek 'antipátheia' (ἀντιπάθεια, feeling against), and 'antithesis' from 'antíthesis' (ἀντίθεσις, opposition, a placing against).
Greek Origins
During the Renaissance and the Scientific Revolution, the prefix became enormously productive as scholars coined new technical terms directly from Greek elements. 'Antiseptic' (against putrefaction), 'antigen' (generating an antibody response), 'antibiotic' (against life, i.e., against microorganisms), and 'antihistamine' all emerged from this learned tradition of Greek-based word formation.
The nineteenth and twentieth centuries saw 'anti-' break free from its learned origins and become a living English prefix that speakers freely attach to any word, including native English words and even proper nouns. 'Antiwar,' 'antifreeze,' 'antihero,' 'antisocial,' 'antitrust,' 'anti-government,' and 'anti-establishment' demonstrate this productive freedom. The prefix can now attach to virtually any noun or adjective to create a new compound meaning 'opposed to' or 'the opposite of' that thing.
Some 'anti-' words conceal their prefix through sound changes. 'Anthem' comes from Greek 'antíphōna' (ἀντίφωνα, things sounding in response), an antiphonal chant; the word lost its prefix-feeling entirely as it evolved through Old English 'antefn.' 'Antarctic' combines 'anti-' with 'arktikós' (ἀρκτικός, of the bear, northern), referring to the constellation Ursa Major that marks the north — Antarctica is literally 'the opposite of the bear-land,' the region opposite the Arctic.
Later Development
The word 'antagonist' embeds the same root: from Greek 'antagōnistḗs' (ἀνταγωνιστής), from 'anti-' + 'agōnízesthai' (to contend), literally 'one who contends against.' Every villain in every story is etymologically someone who stands face-to-face against the protagonist ('prōtos' + 'agōnistḗs,' the first contender).
The prefix should not be confused with 'ante-' (Latin, meaning 'before,' as in 'antecedent,' 'anteroom,' 'antebellum'), though the two share a distant PIE ancestor. Both descend from *h₂enti, but Greek developed the 'against' sense while Latin preserved the 'before/in front of' sense. The occasional confusion between the two prefixes in English — people writing 'anti-room' for 'anteroom' — reflects this shared ancestry and similar sound.
In contemporary English, 'anti-' has become so common that it functions almost as an independent word. People describe themselves as 'anti' something without needing a second element, and the prefix has spawned the standalone noun 'anti' (a person opposed to something). This evolution from bound prefix to free-standing word represents one of the most complete journeys a morpheme can make in a language — from a PIE root meaning 'face' to a Greek preposition meaning 'against' to an English word meaning 'opponent.'