'anti-protozoal' originates from Greek elements 'anti-' and 'protozoon', where 'anti-' meant 'against', 'protos' meant 'first' and 'zoon' meant 'animal'.

'protozoon' (Greek) became Latin/modern 'protozoa' (plural) and formed the adjective 'protozoal' with the English suffix '-al'; medical English then combined the prefix 'anti-' + 'protozoal' (20th century usage) to form 'anti-protozoal'.

Initially it referred specifically to agents directed 'against protozoa'; over time the term has remained specialized in medical and pharmacological contexts with essentially the same meaning: 'effective against protozoal organisms'.