professorship vs chair

professorship and chair both are nouns.

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

As nouns, professorship and chair are synonyms defined as:

professorship (noun)	chair (noun)
the position of professor	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

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