Noun.
Depending on how you use it, it can be a verb ("I like to FISH") or a noun ("I caught a FISH").
A part of speech -- there are eight -- defines the classification of a word. For example, run is a verb, house is a noun and so forth. A figure of speech is a phrase used for emphasis which is not...
"They" is the third person plural personal pronoun of English in its nominative case.
Preposition