The word eavesdropper existed before the word eavesdrop. Yep, our current word for "to listen in on others" is actually a seventeenth-century back-formation from a previous term meaning "one who listens at walls or windows". This in turn was created from the noun eavesdrip, which is the "place where water drips off the roof". Thus, an eavesdropper is someone who hides near an eavesdrip and listens to conversations going on inside. The first part of that, eaves, is a word that still exists today, meaning "lower part of a roof". Eaves, through Old English efes and Proto-Germanic ubaswo, derives from the Proto-Indo-European reconstruction upo, or "under". Drip, obviously, we also have in our vernacular. It traces to Proto-Indo-European dhreu through Proto-Germanic drupjanan, both with the same meaning. The word eavesdrop has been increasing exponentially in recent years, as people have been getting nosier, I guess.
Hello! I'm Adam Aleksic. This year, I graduated from Harvard University with a degree in Government and Linguistics. There, I co-founded the Harvard Undergraduate Linguistics Society and wrote a thesis on Serbo-Croatian language policy, magna cum laude. In addition to etymology, I also really enjoy philosophy, trivia, vexillology, geography, board games, conlanging, art history, and law.