Is the word their an adverb?

No, "their" is not an adverb. It is a possessive pronoun, which means it shows ownership.

Here's a breakdown:

* Adverbs modify verbs, adjectives, or other adverbs, telling us how, when, where, or to what extent something happens.

* Pronouns take the place of nouns, and possessive pronouns show who or what something belongs to.

Examples:

* Adverb: "The bird flew quickly." (Quickly modifies the verb "flew")

* Possessive Pronoun: "The dog wagged its tail." (Its shows ownership of the tail)