mourner vs pallbearer

mourner and pallbearer both are nouns.

Word	Noun	Adjective	Verb	Adverb
mourner	Yes	No	No	No
pallbearer	Yes	No	No	No

As nouns, pallbearer is a hyponym of mourner; that is, pallbearer is a word with a more specific, narrower meaning than mourner:

mourner: a person who is feeling grief (as grieving over someone who has died)
pallbearer: one of the mourners carrying the coffin at a funeral

Other hyponyms of mourner include bearer, wailer, weeper.

mourner (noun)	pallbearer (noun)
a person who is feeling grief (as grieving over someone who has died)	one of the mourners carrying the coffin at a funeral