Adjectives – Suitable Adjective for ‘Bear’

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.

One thing that might help you is to know that often when an adjective and noun are combined to become a noun, there is a hyphen between the words, though the hyphen tends to get dropped as the compound comes into more general usage. The spellcheck on your computer may give you. I can't document this, but it seems to me that spellchecks tend to lag a bit behind general usage and keep the hyphen longer. Otherwise you just have to go with common sense and the context in which the words are used.