Definition of look out in US English:

look out

phrasal verb

  • usually in imperative Be vigilant and take notice.

    ‘“Look out!” warned Billie, seeing a movement from the room beyond’
    ‘look out for the early warning signals’
    • ‘‘Look out! Look out!’ they cried to their fellow crew members.’
    • ‘I just hope they will take notice of warning signs we have put up and look out for them on the roads.’
    • ‘Look out for signs of disease.’
    • ‘‘Look out!’ I yelled, diving toward Scott.’
    • ‘As she lived and worked in the rainforest of Ecuador, she had to look out for poisonous snakes, insects and plants.’
    beware, watch out, be on guard, be on one's guard, be alert, be wary, be vigilant, be careful, be cautious, pay attention, take heed, heed, keep one's eyes open, keep one's eyes peeled, keep one's eyes skinned, keep an eye out, be on the qui vive
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