Is there a word for the word being described by an adjective?

Solution 1:

The word modificand exists as a term of art for the thing you are looking for, and means according to the OED, “something that is to be modified.” But it is not particularly common:

A. 1832 Bentham Language Wks. 1843 VIII. 317/2 ― In this way, modificative clauses in any number may be made to precede, and by that means exclusively attach upon one and the same modificand.

The problem with just calling it a noun or noun phrase is that when you have something like

my earlier someone

(Which I would still call an NP, mind you), then the adjective earlier is targeting a pronoun, not a noun, and the possessive determiners my falls in the normal slot in an NP, despite it having a pronoun not a noun at its head.

Solution 2:

The word is noun or noun phrase.