vigilant
[adjective]
Synonyms: watchful, alert, attentive, careful, cautious, circumspect, on one's guard, on the lookout, wakeful

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Contrasted words: lax, neglectful, negligent, remiss, slack, forgetful, oblivious, unmindful
Related Idioms: on one's guard, with a weather eye open
Related Words: agog, anxious, avid, eager, keen, acute, sharp, sharp-eyed, attentive

[TahlilGaran] English Synonym Dictionary ▲

vig‧i‧lant /ˈvɪdʒələnt, ˈvɪdʒɪlənt/ adjective
[Date: 1400-1500; Language: Latin; Origin: present participle of vigilare 'to stay awake, keep watch', from vigil; ⇒ vigil]
giving careful attention to what is happening, so that you will notice any danger or illegal activity:
Please remain vigilant at all times and report anything suspicious.
—vigilantly adverb

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In everyday English, people usually use the expression watch out rather than be vigilant:
We were told to watch out for anything suspicious.

[TahlilGaran] Dictionary of Contemporary English ▲

vigilant
adj.
VERBS be, keep, remain, stay | become
ADV. especially, extra, extremely, particularly, very | constantly, ever The organization is ever vigilant for threats to the habitats of birds.
PREP. about Be extra vigilant about what you eat or drink.
against You need to be vigilant against garden pests.

[TahlilGaran] Collocations Dictionary ▲