big idea

WordReference Random House Unabridged Dictionary of American English © 2025

big′ ide′a, [Informal.]

1. any plan or proposal that is grandiose, impractical, and usually unsolicited:
   You're always coming around here with your big ideas.
2. purpose;
   intention;
   aim:
   What's the big idea of shouting at me?

• 1920–25, American.