What part of speech is the word foul it an adjective?

The word "foul" can be both an adjective and a verb, depending on how it's used in a sentence.

Adjective: "The air smelled foul." (Describes the smell)

Verb: "The player fouled the opponent." (An action, meaning to commit a rule violation)

So, to answer your question, yes, "foul" can be an adjective, but it can also be a verb.