You’re on a train or at a cafe. A juicy bit of conversation catches your ear. You pretend to mind your book or your phone. Secretly, though, you go on eavesdropping. Does our auditory snooping actually have anything to do with the eaves of our houses? In fact, it has everything to do with them, etymologically speaking.
Eavesdrop comes from the Old English yfesdrype, which the Oxford English Dictionary attests all the way back in an 868 Kentish charter. Yfesdrype, or eavesdrip, first referred to the space around a house where rainwater dripped from the eaves. It also named the dripping itself. We see a similar concept in other languages, like the Old Norse upsar-dropi.
That Kentish charter, based on yet more ancient customs, stipulated new buildings couldn’t be constructed within two feet of this space, else the neighboring property would be liable to damage by the ensuing eavesdrip, or eavesdrop. By Middle English, the form eavesdrop supplanted the original eavesdrip.
Eavesdroppers started poking about in the record by the late 15th century. They stood at walls or under windows – within the house’s eavesdrop – to secretly listen in on the private conversations inside. By the early 1600s, probably as back-formed from eavesdropper, we have the modern, general verb to eavesdrop, whether from under literal eaves or not.
Eaves, finally, didn’t begin as a plural form of eave. Its Old English forebear, efes, was singular, but that pesky, final -s was mistaken as a plural in modern English. It’s an understandable error, though, and one that made pea the singular of the etymologically singular pease, cherry of cherise, and possibly shimmy of chemise. I suppose it’s matter of…s-dropping.