Is a noun or pronoun?

"A" is an article. It is a word that comes before a noun to specify whether it is singular or plural and whether it is definite or indefinite.

* Indefinite article: "a" (for words beginning with a consonant sound) and "an" (for words beginning with a vowel sound)

* Definite article: "the"

Here's an example:

* A cat (indefinite article)

* The cat (definite article)