Bony means so thin that the bones show. Bony fingers, a bony face, bony shoulders.
It describes thinness that reveals the frame beneath, and it is unflattering about people while being neutral about fish — a bony fish is one full of small bones to pick out. In anatomy, bony simply means consisting of bone: the bony orbit, a bony ridge. Note that bony and boney are both seen, with bony the standard spelling despite the missing e.
1adjectivebonySo thin that the bones show.
“The bony hands were about all he remembered.”
2adjectivefullFull of bones, of fish.
“I never order trout because it's too bony, and I hate picking the little bits out.”
bony is a quality of thinness.
Bone plus -y, attested in Middle English. Bone is Old English and Germanic, with no relatives outside that family, which is unusual for a body word.
Middle English
bony
English, today
bony
From Middle English bony, equivalent to bone + -y.
Etymology from Wiktionary, CC BY-SA