incumbent vs holder

incumbent and holder both are nouns.

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

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

Other hypernyms of incumbent include functionary, official.

incumbent (noun)	holder (noun)
the official who holds an office	a holding device
	the person who is in possession of a check or note or bond or document of title that is endorsed to him or to whoever holds it
	a person who holds something

incumbent (adjective)	holder (adjective)
currently holding an office
necessary (for someone) as a duty or responsibility; morally binding
lying or leaning on something else