'antianthrax' is a modern English compound formed from the prefix 'anti-' (from Greek 'anti-' meaning 'against') and 'anthrax' (from Greek 'ἄνθραξ' meaning 'coal' or 'carbuncle', later used for the disease).

'anthrax' came into English via Latin/Medieval Latin 'anthrax' from Greek 'ἄνθραξ'; 'anti-' comes from Greek 'anti-' through Latin and has long been used to form compounds, yielding the modern compound 'antianthrax'.

Initially, 'anthrax' referred to a carbuncle/coal-like lesion and then to the disease; 'antianthrax' has been used to denote something 'against anthrax' and has retained that specific protective/combatting sense.