mastoid bone vs appendage

mastoid bone and appendage both are nouns.

Word	Noun	Adjective	Verb	Adverb
mastoid bone	Yes	No	No	No
appendage	Yes	No	No	No

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

mastoid bone: process of the temporal bone behind the ear at the base of the skull
appendage: a natural prolongation or projection from a part of an organism either animal or plant

Other hypernyms of mastoid bone include outgrowth, process.

mastoid bone (noun)	appendage (noun)
process of the temporal bone behind the ear at the base of the skull	a part that is joined to something larger
	an external body part that projects from the body
	a natural prolongation or projection from a part of an organism either animal or plant