word usage - etymology of eavesdropping

there's this word eavesdropping or eavesdrop, which I looked over in oxford and several other places. the closest I got to understanding it was that it originated from an obsolete noun "eavesdrop", meaning the ground on to which water drips from the eaves. But how did come to it's current usage? I'm curious. anyone else?

Answer

There was an ancient custom that stopped a landowner from building within two feet of his boundary, for fear that the water cascading off the eaves might cause problems for his neighbor. By the end of the medieval period, the word eavesdropper had been invented to describe someone who stood within this strip of ground, under the projecting eaves and close to the walls of a building, in order to listen surreptitiously to the conversations within. The verb eavesdrop in the same sense came along about a century later.

The most complete explanation I've found is here

Eavesdrop, or originally eavesdrip, was originally a noun referring to the water dripping off the eaves of a building or ground on which such water would fall. From medieval times there were legal restrictions on building close to one’s property line so that the eavesdrop would not damage the neighbor’s land. From the Kentish Charter of year 868 (yfæs drypæ = eavesdrip):

"An folcæs folcryht to lefænne rumæs butan twigen fyt to yfæs drypæ." (A right of the people to live without restraint except it is uncertain in the eaves drip.)

The word eavesdropper, meaning one who stands in the eavesdrop of a building and listens to conversations within, dates to 1487. From the Nottingham Borough Records of that year, mostly in Latin except for the word in question:

"Juratores...dicunt...quod Henricus Rowley...est communis evys-dropper et vagator in noctibus." (The court…was told…under oath that Henry Rowley…is a common eavesdropper and a prowler in the night.)

Or for a fully English quote, we go to c.1515 and Richard Pynson’s Modus Tenendi Curiam Baronis:

"Avb, Euesdroppers vnder mennes walles or wyndowes...to bere tales."

The verb to eavesdrop makes is not recorded until 1606. It’s not certain whether it’s a backformation of eavesdropper, or if that noun comes from the verb which existed, unrecorded, in earlier years. From the 1606 comedic play Sir Gyles Goosecappe:

"We will be bold to evesdroppe."

If a man set himself to listen through a window or keyhole to what was going on in a house he had to stand so close that the eavesdropping would fall upon him, for which reason all prying persons, seeking by secret means what they have no business to know, came to be called eavesdroppers. It was a punishable crime.

(Source: Oxford English Dictionary, 2nd Edition.)