Origin: before 900; (noun) Middle English evesdrope,evesdripe,Old English yfesdrype; as v., probably back formation from eavesdropper,late Middle English evisdroppyr, apparently literally, one who stands on the eavesdrop in order to listen to conversations inside the house; see eave, drop, drip
(intr) to listen secretly to the private conversation of others
[C17: back formation from earlier evesdropper, from Old English yfesdrype water dripping from the eaves; see eaves, drop; compare Old Norse upsardropi]
late 15c., from O.E. yfesdrype "place around a house where the rainwater drips off the roof," from eave (q.v.) + drip. Technically, "one who stands at walls or windows to overhear what's going on inside."