What part of speech is word lake?

"Lake" can be two different parts of speech depending on how it's used:

* Noun: When referring to a body of water, "lake" is a noun. For example: "We went swimming in the lake."

* Verb: "Lake" can also be a verb, meaning "to form a lake," or "to deposit something in a lake." For example: "The melted snow laked in the valley."

So, to determine the part of speech, you need to look at the sentence it's used in.