niche vs apsis

niche and apsis both are nouns.

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

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

niche: an enclosure that is set back or indented
apsis: a domed or vaulted recess or projection on a building especially the east end of a church; usually contains the altar

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

niche (noun)	apsis (noun)
an enclosure that is set back or indented	a domed or vaulted recess or projection on a building especially the east end of a church; usually contains the altar
a small concavity
a position particularly well suited to the person who or organization which occupies it
(ecology) the status of an organism within its environment and community (affecting its survival as a species)