hard-on vs member

hard-on and member both are nouns.

Word	Noun	Adjective	Verb	Adverb
hard-on	Yes	No	No	No
member	Yes	No	No	No

As nouns, member is a hypernym of hard-on; that is, member is a word with a broader meaning than hard-on:

Other hypernyms of hard-on include penis, phallus.

hard-on (noun)	member (noun)
an erect penis	an external body part that projects from the body
	the male sex organ
	an organization that is a member of another organization (especially a state that belongs to a group of nations)
	one of the persons who compose a social group (especially individuals who have joined and participate in a group organization)
	anything that belongs to a set or class