'diphtheria-preventing' originates from modern English, specifically the combination of 'diphtheria' (the disease name) and 'preventing' (the present participle of 'prevent'), where 'diphtheria' refers to the disease characterized by a membranous throat lesion and 'prevent-' meant 'to keep from happening.'

'diphtheria' comes from Greek 'diphthera' meaning 'leather' (referring to the membrane formed in the throat); the disease name entered medical Latin and then English as 'diphtheria'. 'Prevent' derives from Latin 'praevenire' ('prae-' meaning 'before' + 'venire' meaning 'to come'), passed into Old French and Middle English as forms like 'prevenir'/'preven' and became Modern English 'prevent' and its participle 'preventing'. The compound 'diphtheria-preventing' is a modern English formation combining the disease name and the participle.

Initially, 'diphtheria' referred to a leathery membrane in the throat and 'prevent' originally meant 'to come before' or 'to act beforehand'; over time the components combined in Modern English to form a descriptive compound meaning 'serving to prevent diphtheria.'