Origin and history of spy

mid-13c., spien, "to watch stealthily," from Old French espiier "observe, watch closely, spy on, find out," probably from Frankish *spehon or some other Germanic source, from Proto-Germanic *spehon- (source also of Old High German *spehon "to look out for, scout, spy," German spähen "to spy," Middle Dutch spien). These are the Germanic survivals of the productive PIE root *spek- "to observe."

Old English had spyrian "make a track, go, pursue; ask about, investigate," also a noun spyrigend "investigator, inquirer." Italian spiare, Spanish espiar also are Germanic loan-words.

The meaning "catch sight of, discover at a distance or from a place of concealment" is from c. 1300. The intransitive meaning "play the spy, conduct surveillance" is from mid-15c. The children's game I spy was so called by 1946.

mid-13c., spie, "one who keeps constant watch on another, one sent out to make secret observations," from Old French espie "spy, look-out, scout" (Modern French épie), probably from a Germanic source related to spy (v.). Also compare Middle Dutch spie. Spymaster is attested by 1943.