The verb "spy" occurs in the 1200s meaning "to watch stealthily"; it comes from either Old Frenchespiier "to observe or watch closely" or from Old English spyrian "to make a track, pursue, investigate." The meaning "catch sight of" occurs around 1300, while the intransitive version "to conduct surveillance" is from the mid 1400s. The noun "spy" "one sent out to observe secretly" comes from the same source; the oxford english dictionary lists its earliest written evidence as occuring in the Bible (Genesis and Exodus), with the first use of the verb in a Northumbrian poem called "Cursor Mundi." Links.NightCafe Image Source