stair vs corbel step

stair and corbel step both are nouns.

Word	Noun	Adjective	Verb	Adverb
stair	Yes	No	No	No
corbel step	Yes	No	No	No

As nouns, corbel step is a hyponym of stair; that is, corbel step is a word with a more specific, narrower meaning than stair:

stair: support consisting of a place to rest the foot while ascending or descending a stairway
corbel step: (architecture) a step on the top of a gable wall

Other hyponyms of stair include corbie-step, corbiestep, crow step.

stair (noun)	corbel step (noun)
support consisting of a place to rest the foot while ascending or descending a stairway	(architecture) a step on the top of a gable wall