A pronoun (a cover term) is a °personal pronoun, or an °interrogative pronoun, or a °demonstrative pronoun, or an °indefinite pronoun, or a °relative pronoun.
It does not seem to be possible to define "pronoun" in a non-enumerative way. Note that pronouns need not be nominal, but can be adjectival, adverbial, and even verbal. Adverbial pronouns are often called "pronominal adverbs", or "pro-adverbs", and similarly for "pro-adjectives" and "pro-verbs", and if this usage is adopted, then "pronoun" is replaced by "pro-form". However, it has never been widely adopted by linguists, so here "pronoun" is used in a broad sense, with no relation to "noun". (See also this blogpost: https://dlc.hypotheses.org/2575)