* Noun: When referring to male deer, it's a noun. Example: "The bucks were grazing in the meadow."
* Noun: It can also be slang for dollars. Example: "I spent a couple of bucks on coffee."
* Verb: While less common, "bucks" can be a verb meaning "to give or earn money". Example: "He bucks up for the cause."
To determine the part of speech, you need to look at the context of the sentence.