incumbent vs official

incumbent and official both are nouns.

Word	Noun	Adjective	Verb	Adverb
incumbent	Yes	Yes	No	No
official	Yes	Yes	No	No

As nouns, official is a hypernym of incumbent; that is, official is a word with a broader meaning than incumbent:

Other hypernyms of incumbent include holder, functionary.

incumbent (noun)	official (noun)
the official who holds an office	someone who administers the rules of a game or sport
	a worker who holds or is invested with an office

incumbent (adjective)	official (adjective)
currently holding an office	having official authority or sanction
necessary (for someone) as a duty or responsibility; morally binding	of or relating to an office
lying or leaning on something else	verified officially
	(of a church) given official status as a national or state institution
	conforming to set usage, procedure, or discipline