to be alertly on the lookout, look attentively, or observe, as to see what comes, is done, or happens: to watch while an experiment is performed.
2.
to look or wait attentively and expectantly (usually fol. by for): to watch for a signal; to watch for an opportunity.
3.
to be careful or cautious: Watch when you cross the street.
4.
to keep awake, esp. for a purpose; remain vigilant, as for protection or safekeeping: to watch with a sick person.
5.
to keep vigil, as for devotional purposes.
6.
to keep guard: She was assigned to watch at the door.
–verb (used with object)
7.
to keep under attentive view or observation, as in order to see or learn something; view attentively or with interest: to watch a play; to watch a football game.
8.
to contemplate or regard mentally: to watch his progress.
9.
to look or wait attentively and expectantly for: to watch one's opportunity.
10.
to guard, tend, or oversee, esp. for protection or safekeeping: to watch the baby.
–noun
11.
close, continuous observation for the purpose of seeing or discovering something: Their watch for the birds was unrewarding.
12.
vigilant guard, as for protection or restraint: to keep watch for prowlers.
13.
a keeping awake for some special purpose: a watch beside a sickbed.
14.
a period of time for watching or keeping guard: to stand the first watch.
15.
a small, portable timepiece, as a wrist watch or pocket watch.
16.
a chronometer.
17.
Nautical.
a.
a period of time, usually four hours, during which one part of a ship's crew is on duty, taking turns with another part.
b.
the officers and crew who attend to the working of a ship for an allotted period of time.
18.
one of the periods, usually three or four, into which the night was divided in ancient times, as by the Greeks or Hebrews: the fourth watch of the night.
19.
a person or group that watches, as a lookout, guard, or sentinel: A watch was posted at sunset.
20.
Also called storm watch.Meteorology. an announcement from the U.S. National Weather Service alerting the public that dangerous weather conditions are a possibility and that vigilance and precautionary preparations are advised: hurricane watch, tornado watch. Compare advisory(def. 5), warning(def. 3).
21.
a flock of nightingales.
—Verb phrases
22.
watch out, to be on one's guard; be cautious: Watch out for cars when you cross the road.
23.
watch over, to guard for protection or safekeeping: She watched over us like a mother hen over her brood.
—Idioms
24.
on the watch, vigilant; alert: The hunter was on the watch for game.
25.
watch oneself,
a.
to be cautious.
b.
to practice discretion or self-restraint.
Origin: bef. 900; 1580–90 for def. 15;(v.) ME wacchen, OE wæccan, doublet of wacian to be awake (see wake1); (n.) ME wacche, OE wæcce, deriv. of wæccan
Synonyms: 1.Watch,look,see imply being aware of things around one by perceiving them through the eyes. To watch is to be a spectator, to look on or observe, or to fix the attention upon during passage of time: to watch while a procession passes. To look is to direct the gaze with the intention of seeing, to use the eyesight with attention: to look for violets in the spring; to look at articles displayed for sale. To see is to perceive with the eyes, to obtain a visual impression, with or without fixing the attention: animals able to see in the dark. 9.await. 10.protect. 11.inspection, attention. 12.vigil.
[woch] 
