'non-painful' originates from a combination of the prefix 'non-' and the adjective 'painful'. 'non-' comes from Latin 'non' meaning 'not', and 'painful' derives from English 'pain' + suffix '-ful', where 'pain' traces back to Old French 'peine' and Latin 'poena'.

'pain' came into English via Old French 'peine' (from Latin 'poena' meaning 'penalty' or 'punishment'). The adjective 'painful' was formed in English with the suffix '-ful'. In Modern English compounds and negated forms like 'non-painful' were created by adding the productive prefix 'non-' to existing adjectives.

Originally the Latin 'poena' primarily meant 'punishment' or 'penalty'; over time its descendant 'pain' shifted to primarily mean physical suffering. 'Non-painful' therefore came to mean 'not causing physical suffering' in modern usage.