successor vs heir

successor and heir both are nouns.

Word	Noun	Adjective	Verb	Adverb
successor	Yes	No	No	No
heir	Yes	No	No	No

As nouns, successor and heir are synonyms defined as:

successor (noun)	heir (noun)
a thing or person that immediately replaces something or someone	a person who is entitled by law or by the terms of a will to inherit the estate of another
a person who inherits some title or office	a person who inherits some title or office
a person who follows next in order