'streamlined-finned' originates from modern English as a compound of 'streamlined' and 'finned', where 'streamlined' comes from 'streamline' meaning 'to give a shape that reduces fluid resistance' and 'fin' means 'a wing-like appendage used for steering or stability'.

'streamline' is a 20th-century engineering coinage (early 1900s), formed from 'stream' + 'line' to describe shapes that follow smooth flow; 'fin' goes back to Old English and related Germanic words for the fin of a fish, later used in mechanical contexts as 'finned' to describe appended surfaces.

Initially, the elements described separate concepts—'streamline' as a design principle and 'fin' as a body part or surface—but over time the compound came to specifically denote objects whose fins are shaped or arranged to achieve streamlined (low-drag) performance.