Definition
Vigilant means awake while others sleep — from the Latin vigilare, 'to keep watch'. The vigilant lifeguard, auditor, or immune system is defined by what usually doesn't happen: the drowning prevented, the fraud caught early, the infection stopped at the gate. Vigilance looks like boring routine for hours and proves itself in a single second; the word always implies sustained attention paid before anything has gone wrong.
Examples
- Lifeguards must remain vigilant even when the water looks calm.
- Regulators are urging banks to be more vigilant against online fraud.
- Thanks to a vigilant neighbor, the fire was reported within minutes.
Synonyms
watchful · alert · attentive · wary · observant
In TOEFL & IELTS
Frequent in IELTS reading and listening on safety, health, and security — and 'remain/stay vigilant' is the collocation officials use in every public warning, making it natural for essays on crime or online privacy. TOEFL passages apply it to immune systems and sentinel animals. Noun: vigilance; do not confuse with 'vigilante', someone who enforces the law themselves.