The definition of vigilant is watchful and alert.(adjective)
An example of something vigilant is a guard dog.
See vigilant in Webster's New World College Dictionary
Origin: Fr < L vigilans, prp. of vigilare, to watch < vigil, awake: see vigil
See vigilant in American Heritage Dictionary 4
Origin: Middle English
Origin: , from Old French
Origin: , from Latin vigilāns, vigilant-
Origin: , present participle of vigilāre, to be watchful; see vigilante.
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