The word first *is* an adjective (number one in order, or primary) - e.g. his first car.
Ordinal numbers such as first can also be nouns (e.g. a first, the first).
The adjective form of concept is conceptual.The adjective form of conception is conceptional.
The adjective form is cranial.
The adjective form for the pronoun they is their.
The Adjective form of Pathologist is Pathological.
The adjective form of concept is conceptual.The adjective form of conception is conceptional.
The adjective form of improve is "improved."
First is a superlative adjective. It has no non-superlative form, although you could use "primary" in this way ("most primary" being equivalent to "first" or "foremost").
The adjective form for the verb to develop is developable.
The plural form of the noun 'adjective' is adjectives.
The adjective form of retire is :- retired, retiring.
The adjective form is patient.
Precarious is the adjective form.