stair vs tread

stair and tread both are nouns.

Word	Noun	Adjective	Verb	Adverb
stair	Yes	No	No	No
tread	Yes	No	Yes	No

stair (noun)	tread (noun)
support consisting of a place to rest the foot while ascending or descending a stairway	a step in walking or running
	structural member consisting of the horizontal part of a stair or step
	the part (as of a wheel or shoe) that makes contact with the ground
	the grooved surface of a pneumatic tire

stair (verb)	tread (verb)
	crush as if by treading on
	brace (an archer's bow) by pressing the foot against the center
	mate with (used of male birds)
	tread or stomp heavily or roughly
	put down or press the foot, place the foot
	apply (the tread) to a tire