sinewy adj. + Add to list US //ˈsɪnjui// UK //sˈɪnjuːi// sinewy SynonymsEtymology Synonyms brawnyfibrousheftymuscularpowerfulstringytendinousunchewableOriginMEsynwy→ENsinewy Inherited from Middle English synwy, synewy, synowy (“tendonous”); equivalent to sinew + -y.