'antiparasitical' is formed from the prefix 'anti-' (from Greek 'anti' meaning 'against') + 'parasitical' (relating to 'parasite'). In English the combination expresses 'against parasites'.

'parasite' originates from Greek 'parasitos' ("one who eats at another's table") which passed into Latin as 'parasitus', then into Old French and Middle English as 'parasite'; 'parasitic' and 'parasitical' developed from that base, and English later formed compounds with the prefix 'anti-' to create 'antiparasitic/antiparasitical'.

Originally 'parasitos' meant 'one who eats at another's table' (a person who sponged food); over time the term shifted to describe organisms that live on or in a host and derive nutrients from it. 'Antiparasitical' therefore came to mean 'opposed to or destroying such organisms'.