skull vs bone

skull and bone both are nouns.

Word	Noun	Adjective	Verb	Adverb
skull	Yes	No	No	No
bone	Yes	Yes	Yes	No

As nouns, bone is a hypernym of skull; that is, bone is a word with a broader meaning than skull:

Other hypernyms of skull include os.

skull (noun)	bone (noun)
the bony skeleton of the head of vertebrates	a shade of white the color of bleached bones
	rigid connective tissue that makes up the skeleton of vertebrates
	the porous calcified substance from which bones are made

skull (adjective)	bone (adjective)
	consisting of or made up of bone

skull (verb)	bone (verb)
	remove the bones from
	study intensively, as before an exam