'parasite-killing' is a compound formed from 'parasite' and the present-participial form 'killing' of the verb 'kill'. 'parasite' originates from Greek, specifically the word 'parasitos', where 'para-' meant 'beside' and 'sitos' meant 'food'. 'kill' originates from Old English, ultimately from Germanic roots meaning 'to cause death.'

'parasite' passed from Greek 'parasitos' into Late Latin 'parasitus' and Old French before entering Middle English as 'parasite'; 'kill' was present in Old English (e.g. 'cwellan' meaning to kill) and developed into the Modern English 'kill'. The compound 'parasite-killing' is a modern English formation combining the noun and a participial form.

Initially 'parasite' meant 'one who eats at another's table' in Greek, but over time it shifted to the biological sense 'an organism that lives on or in a host and benefits at the host's expense'; 'kill' has largely retained the sense 'to cause death'. The compound now specifically denotes the action or property of destroying parasites.