sinus rectus vs sinus

sinus rectus and sinus both are nouns.

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

As nouns, sinus is a hypernym of sinus rectus; that is, sinus is a word with a broader meaning than sinus rectus:

sinus rectus: an unpaired sinus of the dura mater
sinus: a wide channel containing blood; does not have the coating of an ordinary blood vessel

Other hypernyms of sinus rectus include venous sinus.

sinus rectus (noun)	sinus (noun)
an unpaired sinus of the dura mater	a wide channel containing blood; does not have the coating of an ordinary blood vessel
	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