kapı kolu (door handle, but literally it translates to arm of the door).
I recently read Nicholas Kristoff's article, "Go West, Young People! And East!" where he talked about his one word language test for language learners: How do you say door knob? Generally, people who lived abroad did much better than those who simply studied a language in their native country.
Since I've been living in Turkey for almost two years, I figured I had better learn this simple phrase.
Here's the article if you're interested: