Qui vive \Qui` vive"\ [F., fr. qui who + vive, pres. subj. of vivre to live.]

The challenge of a French sentinel, or patrol; -- used like the English challenge: ``Who comes there?''

To be on the qui vive, to be on guard; to be watchful and alert, like a sentinel.

Source: Webster's Revised Unabridged Dictionary (1913)