Achilles tendon vs sinew

Achilles tendon and sinew both are nouns.

Word	Noun	Adjective	Verb	Adverb
Achilles tendon	Yes	No	No	No
sinew	Yes	No	No	No

As nouns, sinew is a hypernym of Achilles tendon; that is, sinew is a word with a broader meaning than Achilles tendon:

Achilles tendon: a large tendon that runs from the heel to the calf
sinew: a cord or band of inelastic tissue connecting a muscle with its bony attachment

Other hypernyms of Achilles tendon include tendon.

Achilles tendon (noun)	sinew (noun)
a large tendon that runs from the heel to the calf	possessing muscular strength
	a cord or band of inelastic tissue connecting a muscle with its bony attachment