'fin-equipped' originates from Modern English as a compound of 'fin' and the past participle 'equipped'; 'fin' ultimately comes from Old English 'finn' (related to Old Norse) meaning 'fin', and 'equip' comes from Old French 'equiper', from Latin 'aequipare', where 'aequi-' meant 'equal' and 'parare' meant 'to make ready'.

'fin' continued from Old English 'finn' into Modern English as 'fin'; 'equip' evolved from Latin 'aequipare' to Old French 'equiper' and entered Middle English as 'equip', with the past participle form 'equipped' used in compounds like 'fin-equipped'.

Initially the components referred separately to 'fin' (a limb or appendage for swimming) and 'equip' (to outfit or provide); over time the compound came to mean simply 'having or provided with fins' in modern usage.