be on the watch

be carefully looking out for something, especially a possible danger

留心，注意；提防

keep watch

stay on the lookout for danger or trouble

放哨

watch one's (或 someone's) back

protect oneself (or someone else) against danger from an unexpected quarter

保护自己（或他人）（以防意外的危险）

watch one's mouth

the watches of the night

(poetic/literary)the hours of night, portrayed as a time when one cannot sleep

(诗／文)夜间醒着的时间

watch the pennies

watch one's step

watch this space

watch the time

ensure that one is aware of the time in order to avoid being late

注意时间

watch the world go by

spend time observing other people going about their business

观察他人在做什么

watch out

To be careful or on the alert; take care.

戒备：提防或戒备；注意

watch over

To be in charge of; superintend.

监督

watch it

To be careful

注意留神

had to watch it when I stepped onto the ice.

当我走上冰面就不得不留神了

watch (one's) step

To act or proceed with care and caution.

谨慎行事：小心谨慎地行动或前进

To behave as is demanded, required, or appropriate.

按要求或合适地表现