Brawny means physically strong and muscular. A brawny arm, brawny shoulders, big and brawny.
It describes visible bulk rather than trained strength, which is why it suits blacksmiths in fiction. Brawn means muscle, and brains and brawn is the fixed pair. Note that brawn also names a cold meat set in jelly from a pig's head, which is the older sense of the word.
1adjectivebrawnyPhysically strong and muscular.
“Two brawny men carried the piano up three flights of stairs.”
brawny is a quality of build.
Brawn plus -y, from Old French braon, a fleshy part, of Germanic origin. The meat sense is the older one.
Middle English
brawny
English, today
brawny
From Middle English brawny; equivalent to brawn + -y.
Etymology from Wiktionary, CC BY-SA