'reward-sensitive' is a modern English compound formed from 'reward' + 'sensitive'. 'reward' ultimately comes from Middle English 'rewarde' (from Old North French 'reguarde'), where the elements resembled 're-' (back/again) and a Germanic root related to 'guard' meaning 'to watch/guard'. 'sensitive' comes from Latin 'sensitivus', from 'sentire' meaning 'to feel'.

'reward' changed from Old North French 'reguarde' into Middle English 'rewarde' and later became modern English 'reward'. 'sensitive' entered English via Old French/Latin: Latin 'sensitivus' → Old French forms → Middle English 'sensitive' and then modern English 'sensitive'.

Originally, elements of 'reward' conveyed a sense of 'return' or 'regard' and evolved to mean 'something given in return for service or achievement'. 'sensitive' originally meant 'capable of feeling' and broadened to 'responsive to specific stimuli', so together 'reward-sensitive' came to mean 'responsive to rewards'.