'antidiphtherin' originates from Neo-Latin/scientific coinage, formed from Greek elements 'anti-' meaning 'against' and 'diphthera' meaning 'leather' (used for the membranous lesion in diphtheria).

'antidiphtherin' was coined in the late 19th century in medical contexts (influenced by German usage such as 'Antidiphtherin') as serum therapy for diphtheria became established; it entered English medical literature and usage thereafter.

Initially it meant 'a serum that neutralizes diphtheria toxin'; over time the basic meaning has remained, though the term has become largely historical/technical as more general terms like 'diphtheria antitoxin' or 'antitoxin' are now common.