armchair vs chair

armchair and chair both are nouns.

Word	Noun	Adjective	Verb	Adverb
armchair	Yes	No	No	No
chair	Yes	No	Yes	No

As nouns, chair is a hypernym of armchair; that is, chair is a word with a broader meaning than armchair:

armchair (noun)	chair (noun)
chair with a support on each side for arms	the position of professor
	a seat for one person, with a support for the back
	an instrument of execution by electrocution; resembles an ordinary seat for one person
	a particular seat in an orchestra
	the officer who presides at the meetings of an organization

armchair (verb)	chair (verb)
	preside over
	act or preside as chair, as of an academic department in a university