spy

/ˈspī/

Middle English spien, from Anglo-French espier, of Germanic origin; akin to Old High German spehōn to spy; akin to Latin specere to look, look at, Greek skeptesthai & skopein to watch, look at, consider

verb

  1. to watch secretly usually for hostile purposes

  2. to catch sight of : see

  3. to search or look for intensively —usually used with out

noun

  1. one that spies:

  2. one who keeps secret watch on a person or thing to obtain information

  3. a person employed by one nation to secretly convey classified information of strategic importance to another nation; also : a person who conveys the trade secrets of one company to another

phrasal verb

  1. to watch (someone) secretly

He spies on his neighbors.