'parasiticidal' is formed from 'parasite' + the suffix '-cidal' (from Latin roots meaning 'to kill').

'parasite' originates from Greek 'parasitos' (meaning 'one who eats at another's table'); the combining element '-cide'/'-cidal' comes from Latin 'caedere' (to cut, strike down, kill) via Medieval/Modern Latin and French. Modern English formations such as 'parasiticide' and the adjective 'parasiticidal' were created by combining these elements in scientific usage.

Initially the components referred separately to 'parasite' and 'killing'; combined in modern scientific English they specifically denote 'killing parasites' or 'having the quality of killing parasites', a sense that has remained stable in technical use.