president vs chairman

president and chairman both are nouns.

Word	Noun	Adjective	Verb	Adverb
president	Yes	No	No	No
chairman	Yes	No	Yes	No

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

Other hyponyms of president include Kalon Tripa, vice chairman, chairwoman.

president (noun)	chairman (noun)
the chief executive of a republic	the male officer who presides at the meetings of an organization
an executive officer of a firm or corporation
the head administrative officer of a college or university
the officer who presides at the meetings of an organization

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