What's a doughnut? - Click here.

Someone who is crazy about money.

A doughnut is a fried cake shaped like a ring. In slang, dough also means "money", and nut can mean "a crazy or eccentric person". If you are a nut for something, it means that you are extremely enthusiastic about it.

A: Richard, you're looking well. How about getting some coffee with me?

B: Coffee and dougnuts sounds great! So, what have you been up to latetly? I haven't seen you for a while.

A: Actually, I've been working around the clock in my new business.

B: Oh, you're after the big bucks, huh? I never thought you'd be so dedicated to money! You're becoming a real "dough nut"!

A: Yeah, and a health nut, too. I don't eat doughnuts anymore - they have too much fat!

(Harry Collis. 101 American Riddles. Passport Books: 1996.)