'antipestilentially' originates from a combination of Greek and Latin: the prefix 'anti-' from Greek meaning 'against' and the Latin word 'pestilentia' (from 'pestis') meaning 'plague'.

'pestilentia' gave rise to Medieval/Latin adjective forms such as 'pestilentialis' (Late Latin) and entered Middle English via Old French/Latin as 'pestilential'; the prefix 'anti-' was attached and the adverbial suffix '-ly' formed the modern English 'antipestilentially'.

Initially the components meant 'against plague' (literally opposing pestilence); over time the compound has been used more broadly to mean 'in a preventive or prophylactic manner' against infectious or noxious influences.