/ ˈiːvzdrɒp; NAmE -drɑːp/ verb
( -pp- ) [ v ] eavesdrop (on sb/sth) to listen secretly to what other people are saying :
We caught him eavesdropping outside the window.
► eaves·drop·per noun
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WORD ORIGIN
early 17th cent.: back-formation from eavesdropper ( late Middle English ) a person who listens from under the eaves , from the obsolete noun eavesdrop the ground on to which water drips from the eaves , probably from Old Norse upsardropi , from ups eaves + dropi a drop.