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Meaning of big deal

big' deal'

Pronunciation: [key]
— Slang. Slang.
  1. an important or impressive person or thing: to make a big deal out of nothing; I hear he's a big deal on Wall Street now.
  2. (used ironically as an interjection to indicate that one considers something to be unimportant or unimpressive): So you're the mayor's cousin —big deal!
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.