What is the correct term for using a verb as an adjective? [closed]

OP's actual example is invalid - shown, blown, grown, known, thrown are all valid Past Participle forms, but not town or crown (which are "regular" verbs with PP towed and crowed). But if it was a valid, use, it would be called a...

participial adjective (Lexico.com)
An adjective that is a participle in origin and form, such as burned, cutting, engaged.

And thoughtco.com, tells us it's also called a verbal adjective or a deverbal adjective.

Another potentially relevant term from my second link above is pseudo-participial adjective - used to identify the increasing number of adjectives [that] are coined by adding -ing or -ed not to verbs but to nouns. Examples of which include enterprising, neighboring, talented, and skilled (there is no verb to enterprise, for example).