'antiatom' originates from English formation combining the prefix 'anti-' (from Greek 'ἀντί' meaning 'against, opposite') and the noun 'atom' (from Greek 'ἄτομος' atomos meaning 'indivisible').

'anti-' comes from Greek 'ἀντί' and was adopted into English as a productive prefix; 'atom' entered English via Latin/Greek from Greek 'ἄτομος' ('atomos'). The compound 'antiatom' is a modern English coining used after the discovery and naming of antimatter in the 20th century.

Initially formed as a literal compound meaning 'an atom that is opposite (in charge/particle content) to a normal atom'; over time it has been used specifically to refer to atoms made of antimatter (e.g., antihydrogen).