From Old English 'efes' (roof edge) — the projecting part of the roof, and the source of 'eavesdrop.'
The lower edge of a roof that overhangs the wall of a building, providing protection from rain and weather; usually used in the plural as 'eaves.'
From Old English 'efes' (the edge of a roof, eaves), from Proto-Germanic *ubaswo (the overhang, the projection), from PIE *upó (under, up from under). The word is related to the concept of being 'over' or 'above' — the eave is the part of the roof that extends out over the wall. The singular form 'eave' is a back-formation from 'eaves,' which was originally singular (Old English 'efes') but was reinterpreted as a plural because of its final -s. Key
The word 'eavesdrop' literally means to stand under the eaves of a building to listen to conversations inside. In Anglo-Saxon law, the 'eavesdrip' — the strip of ground where rainwater fell from the eaves — was legally significant: building too close to a neighbor's eavesdrip was a punishable offense.