frontal suture vs fibrous joint

frontal suture and fibrous joint both are nouns.

Word	Noun	Adjective	Verb	Adverb
frontal suture	Yes	No	No	No
fibrous joint	Yes	No	No	No

As nouns, fibrous joint is a hypernym of frontal suture; that is, fibrous joint is a word with a broader meaning than frontal suture:

frontal suture: the suture between two halves of the frontal bone (usually obliterated by the age of 6)
fibrous joint: an immovable joint (especially between the bones of the skull)

Other hypernyms of frontal suture include sutura, suture.

frontal suture (noun)	fibrous joint (noun)
the suture between two halves of the frontal bone (usually obliterated by the age of 6)	an immovable joint (especially between the bones of the skull)