'flexible-finned' originates from the combination of 'flexible' and 'finned', where 'flexible' comes from Latin 'flexibilis', meaning 'capable of being bent', and 'finned' refers to having fins.

'Flexible' changed from the Latin word 'flexibilis' and eventually became the modern English word 'flexible'. 'Finned' is derived from the Old English 'finn', meaning 'fin'.

Initially, 'flexible' meant 'capable of being bent', and this meaning has largely remained the same in modern usage.