Ballcock.

Stop it. Just stop it right now. I know, I know. I’m awful. But it’s not what you think, dammit! You’re the one with filthy mind. Shame on you. A ballcock is actually the most mundane object you can imagine. It’s a piece of plumbing equipment, a floating ball that controls the water level in a tank. So there.

The problem is that this perfectly innocent little word sounds very, very naughty, which is of course due to all the well known ribald associations of the words that make up this compound noun. Just reading this word causes the corners of one’s mouth to curl up in a smile.

And I think that’s wonderful. This word makes people happy.