brawn vs sinew

brawn and sinew both are nouns.

Word	Noun	Adjective	Verb	Adverb
brawn	Yes	No	No	No
sinew	Yes	No	No	No

As nouns, brawn and sinew are synonyms defined as:

Other synonyms of brawn include brawniness, heftiness, muscle, muscularity.

brawn (noun)	sinew (noun)
possessing muscular strength	possessing muscular strength
	a cord or band of inelastic tissue connecting a muscle with its bony attachment