Is the sentence Janet was an alternate on the swim team a noun a verb or an adjective?

"Janet was an alternate on the swim team." This is a sentence: each individual Word is a particular part of speech that serves a particular function.

The nouns are:

• Janet; proper noun, subject of the sentence
• alternate; common noun, a predicate noun (also called a subject complement)
• team (or the compound noun 'swim team'), common noun, object of the preposition 'on'

The verb is: was, a linking verb, past tense of the verb to be.

There is no adjective in the sentence.

Note: The Word 'alternate' also functions as an adjective, however, in this sentence it is a noun, a Word for a person named to take the place of another when necessary. In order to function as an adjective, it must be followed by a noun, for example, "Janet was an alternate swimmer on the team."

The Word 'swim' used to form the compound noun 'swim team' is not an adjective either. It is a noun used to describe another noun, a function called an attributive noun.