incumbent vs superjacent

incumbent is a noun but superjacent is not a noun.

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

incumbent (noun)	superjacent (noun)
the official who holds an office

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