vigilant.

Maintaining careful watch for danger, problems, or changes requiring attention.

Use it for

Words that belong together

• remain vigilant
• a vigilant observer

On the page

The vigilant observer noticed the repeated gap in the signal.

She remained vigilant without treating every unfamiliar sound as an alarm.

Usage notes

Primary category: literary. Forms: Comparative more vigilant; superlative most vigilant where gradation is meaningful. Legacy lexical fields mirror sense 1 only. Use numbered sense fields for all meanings.