Vigil
Middle English (in vigil (sense 2)): via Old French from Latin vigilia, from vigil ‘awake’.
wiktionary
From Middle English vigile(“a devotional watching”), from Old French vigile, from Latin vigilia(“wakefulness, watch”), from vigil(“awake”), from Proto-Indo-European *weǵ-(“to be strong, lively, awake”). See also wake, from the same root.
Related to vigor, and more distantly compare vis and vital, from similar Proto-Indo-European roots and meanings (lively, power, life), via Latin. For use of “live, alive” in sense “watching”, compare qui vive.
etymonline
vigil (n.)
c. 1200, "eve of a religious festival" (an occasion for devotional watching or observance), from Anglo-French and Old French vigile "watch, guard; eve of a holy day" (12c.), from Latin vigilia "a watch, watchfulness," from vigil "watchful, awake, on the watch, alert," from PIE root *weg- "to be strong, be lively." Meaning "watch kept on a festival eve" in English is from late 14c.; general sense of "occasion of keeping awake for some purpose" is recorded from 1711.
