mummer vs role player

mummer and role player both are nouns.

Word	Noun	Adjective	Verb	Adverb
mummer	Yes	No	No	No
role player	Yes	No	No	No

As nouns, role player is a hypernym of mummer; that is, role player is a word with a broader meaning than mummer:

Other hypernyms of mummer include actor, histrion, player, thespian.

mummer (noun)	role player (noun)
an actor who communicates entirely by gesture and facial expression	a theatrical performer
	a person who makes deceitful pretenses