Definition from Wiktionary, the free dictionary
French who lives? - a sentry's challenge
- a state of heightened vigilance, especially prior to battle
- Oliver Wendal Holmes. 
- "QUI vive!" The sentry's musket rings,
- The channelled bayonet gleams;
- High o'er him, like a raven's wings
- The broad tri-colored banner flings
- "QUI vive!" The sentry's musket rings,. The channelled bayonet #:gleams; ... "Qui vive!" How oft the midnight air. That startling cry has borne! ...
- 1917 "The Flags of France." Grace Ellery Channing
- Qui vive? Who passes by up there?
- Who moves -- what stirs in the startled air?
- What whispers, thrills, exults up there?
- Qui vive?
- Were a tall black man to do the same, there is not one of us who would not immediately be on the qui vive. My sadness about the American estrangement just mentioned doesn't make me act any differently at such a moment,
- Oliver Wendal Holmes.