fistula vs sinus

fistula and sinus both are nouns.

Word	Noun	Adjective	Verb	Adverb
fistula	Yes	No	No	No
sinus	Yes	No	No	No

As nouns, fistula and sinus are synonyms defined as:

fistula and sinus: an abnormal passage leading from a suppurating cavity to the body surface

fistula (noun)	sinus (noun)
an abnormal passage leading from a suppurating cavity to the body surface	a wide channel containing blood; does not have the coating of an ordinary blood vessel
a chronic inflammation of the withers of a horse	any of various air-filled cavities especially in the bones of the skull
	an abnormal passage leading from a suppurating cavity to the body surface