a noun is a type of word that identifies a person, place, thing, idea, action, or quality. Watch can be used as a noun to refer to a timepiece, like a wristwatch, pocket watch, or wall clock, that tells the time.
when used this way, it typically follows the articles 'a' or 'the', e.g. 'I need to buy a new watch'. It can also be used to refer more generally to the act of keeping an eye on something or someone, like 'I'll be keeping a watch on you'.
I bought a waterproof watch to go swimming.
She put her watch in her purse before she went to bed.
Keep a watch on the house while I'm on vacation.
watch is used as a verb to mean carefully observing or monitoring someone or something. This usage typically implies that the person or thing is being monitored for some sort of change or development.
They were watching his every move.
We will watch the sunrise from the beach.
I need to watch the stock market to see if it rises.