what an idea—
1. that’s a great idea:
- They don’t fit very well under the Christmas tree, but what an idea for that perfect gift!
2. that’s preposterous; that’s most unreasonable:
- Pa looked at ma stunned. Good heavens what an idea!
what’s the idea —(also: what’s the big idea) what’s the intention or purpose (is usually used to question smth. that is not welcome):
- What’s the idea behind creating a game that’s part way between Australian Rules football and Gaelic football.