'pepsin-active' originates from Modern English as a compound combining 'pepsin' and 'active'. 'pepsin' ultimately comes from Greek 'pepsis' meaning 'digestion' (via Neo-Latin 'pepsinum'), and 'active' comes from Latin 'activus' meaning 'active'.

The element 'pepsin' derived from Neo-Latin 'pepsinum', itself from Greek 'pepsis' ('digestion'). 'Active' entered English via Latin 'activus' and Old French 'actif'. In Modern English these elements were combined into the descriptive compound 'pepsin-active' in biochemical contexts.

Originally the components referred separately to 'digestion' (pepsin) and 'being active' (active); over time the compound came to mean specifically 'susceptible to or showing enzymatic action by pepsin'.