1. 警覺的;警惕的
    Someone who is watchful notices everything that is happening.

    e.g. The best thing is to be watchful and see the family doctor for any change in your normal health...
           最佳的做法是保持警惕，一旦你的身體狀況有任何變化就立即去看家庭醫(yī)生。
    e.g. He looked tall and powerful and, with his dark, watchful face, a little threatening.
           他看上去又高又壯，面色黝黑，滿臉警覺，真叫人有點害怕。

2. 在(某人)的警覺目光下；在…的監(jiān)視下
    If you do something under the watchful eye of someone who has authority over you, they watch you carefully to make sure there are no problems.

watchful什么意思

    e.g. There were demonstrations in the streets today, under the watchful eye of police...
           今天，在警方的監(jiān)視下大街上進行了游行。
    e.g. Children swim at the pool, under the watchful eye of lifeguards.
           孩子們在救生員的監(jiān)護下在水池里游泳。

3. 看護;提防
    If you keep a watchful eye on someone or something, you watch carefully to make sure there are no problems.

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    e.g. Keep a watchful eye on babies and toddlers.
           要看好嬰兒和剛會走路的孩子。