niche vs columbarium

niche and columbarium both are nouns.

Word	Noun	Adjective	Verb	Adverb
niche	Yes	No	No	No
columbarium	Yes	No	No	No

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

niche: an enclosure that is set back or indented
columbarium: a niche for a funeral urn containing the ashes of the cremated dead

Other hyponyms of niche include alcove, bay, apse, apsis, cinerarium, fireplace, hearth, open fireplace, mihrab.

niche (noun)	columbarium (noun)
an enclosure that is set back or indented	a sepulchral vault or other structure having recesses in the walls to receive cinerary urns
a small concavity	a niche for a funeral urn containing the ashes of the cremated dead
a position particularly well suited to the person who or organization which occupies it	a birdhouse for pigeons
(ecology) the status of an organism within its environment and community (affecting its survival as a species)