surveillant[-vā′lənt; occas., -vāl′yənt]
surveillant definition by Webster's New World
Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio. Used by arrangement with John Wiley & Sons, Inc.
a person who watches, observes, or supervises
surveillant definition by American Heritage Dictionary
One that exercises surveillance.
Origin: French, present participle of surveiller, to watch over : sur-, over (from Old French; see sur-) + veiller, to watch (from Old French veillier, from Latin vigilāre, from vigil, watchful; see weg- in Indo-European roots).