Definition of qui vive in US English:

qui vive

noun

in phrase on the qui vive
  • On the alert or lookout.

    ‘duty requires the earnest liberal to spend most of his time on the qui vive for fascism’
    alert, awake, watchful, wide awake, observant, perceptive, percipient, acute, aware, noticing, heeding, heedful, mindful, vigilant, on guard, on one's guard, on one's toes, on the qui vive, on the lookout
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Origin

Late 16th century: from French, literally ‘(long) live who?’, i.e. ‘on whose side are you?’, used as a sentry's challenge.

Pronunciation

qui vive

/ˌki ˈviv//ˌkē ˈvēv/