'antipepsin' is a modern compound formed from the prefix 'anti-' (from Greek anti- meaning 'against') and 'pepsin' (from Neo-Latin pepsinum, ultimately from Greek 'pepsis' meaning 'digestion').

'pepsin' was coined in the 19th century from Greek 'pepsis' ('digestion') via Neo-Latin 'pepsinum'; the prefix 'anti-' (Greek) was then attached to form the compound 'antipepsin' in scientific usage to denote something acting against pepsin.

The separate elements originally meant 'against' and 'digestion' respectively; combined in modern usage the term specifically denotes an antibody or inhibitor that acts against the enzyme pepsin.