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mid-13c., from Old French espier "to spy," probably from Frankish *spehon, from Proto-Germanic *spekh- (cf. Old High German *spehon "to look out for, scout, spy," German spähen "to spy," Middle Dutch spien), the Germanic survivals of the productive PIE root *spek- "to look" (see scope (n.1)).
mid-13c., "one who spies on another," From Old French espie, probably from a Germanic source (see spy (v.)).