loose; or yeah...i cant think of any more....bahahahahahahahahaha!
strong
Michelle was slender and tough,with sinewy muscles.
The boy had a sinewy back. Your welcome.
The word "sinewy" is an adjective, used to describe something that is lean and muscular, with well-defined muscles.
I would suggest that "muscle" would be an antonym of sinew. Someone or something that is sinewy is "cut" and lean, so the opposite would be someone that is bulky, or muscular. I have, however, also seen "muscle" listed as a synonym of sinew.
muscular
Pertaining to, consisting of, or resembling, a sinew or sinews., Well braced with, or as if with, sinews; nervous; vigorous; strong; firm; tough; as, the sinewy Ajax.
sinewy, rough, wiry
lean and/or sinewy
Sinewy and soft spring to mind...
strong, vigorous, powerful, muscular, hard, tough, stringy, athletic, sturdy
strong, vigorous, powerful, muscular, hard, tough, stringy, athletic, sturdy