Meaning

noun (military) a secret agent hired by a state to obtain information about its enemies or by a business to obtain industrial secrets from competitors

noun a secret watcher; someone who secretly watches other people

verb catch sight of

originFrom Middle English spien, aphetic variant of earlier espien (“to espy”), from Old French espier (“to spy”), from Frankish *spehōn (“to spy”), from Proto-Germanic *spehōną (“to see, look”), from Proto-Indo-European *speḱ- (“to look”). Akin to German spähen (“to spy”), Dutch spieden (“to spy”). The noun displaced native Old English sċēawere (literally “watcher”), which was also the word for…

Etymology from Wiktionary, CC BY-SA 3.0