big idea

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noun 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?

Origin of big idea

An Americanism dating back to 1920–25 Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018