Eavesdrop

google

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early 17th century: 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’.

wiktionary

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eaves +‎  drop; the "listening" sense derives from the notion of the listener standing in the area denoted by the physical sense. 

etymonline

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eavesdrop (v.)

"lurk near a place to hear what is said inside," c. 1600, probably a back-formation from eavesdropper. The original notion is listening from under the eaves of a house. Related: Eavesdropping.