Eavesdroppers are people who deliberately try to overhear another’s conversation without detection. Centuries ago houses in England had no gutters and drain pipes. Instead the roofs extended far past the walls of the house enabling rainwater to drip to the ground away from the building. The area between the dripping rain and the walls was originally known as the ‘eavesdrip’ and latterly the ‘eavesdrop’.
The eavesdrop also served as a shelter for passing pedestrians who would stand close to the walls of a building and out of the rain, but they could also overhear conversations going on inside a house, and became known as ‘eavesdroppers’.