'antidiphtheritic' originates from the prefix 'anti-' (from Greek anti- 'against') combined with 'diphtheritic' (relating to diphtheria), ultimately from Greek 'diphthera' meaning 'skin, leather' (used of the membrane that forms in the disease).

'antidiphtheritic' was formed in English in the 19th century from New Latin/French formations such as French 'antidiphthéritique' or New Latin 'antidiphtheriticus', combining 'anti-' with 'diphtheritic' (from 'diphtheria'); it entered English medical usage to name remedies or qualities opposing diphtheria.

Initially it meant 'acting against diphtheria' (often applied to sera, vaccines, or remedies), and this basic sense has been retained in modern usage, though the term is now rare and mainly historical or formal.