What is the meaning of the word "watch"?

Definitions:

A fixed period of duty on a ship, usually lasting four hours. NOUN
- Sea air, lots of exercise, and four-hour watches give everyone a healthy appetite.
A period of vigil during which a person is stationed to look out for danger or trouble, typically during the night. NOUN
- My watch lasted from midnight until dawn.
A portable timepiece worn on the wrist or carried in a pocket. NOUN
- She glanced at her watch to check the time.
An act or instance of carefully observing someone or something over a period of time. NOUN
- The security forces have been keeping a close watch on our activities.
Keep under careful, protective, or secret observation. VERB
- There aren't enough staff to watch him properly.
Observe and guard in a protective way. VERB
- I guess I can rest a while, with you here to watch over me.
To be careful of something. VERB
- Watch that you don't get glue on your fingers.
To look at or observe attentively over a period of time. VERB
- I had dinner and watched TV for a couple of hours.