grey matter

• gray matter (US)

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grey matter (uncountable)

1. (idiomatic) Brains; a person's ability to think.
   • 1904, Lucy Maud Montgomery, “Penelope's Party Waist”, in Short Stories: 1904:

     "I'd better be putting my grey matter into that algebra instead of wasting it plotting for a party dress that I certainly can't get."

   • 1914, Sax Rohmer, chapter 10, in The Sins of Severac Bablon:

     "Inspector Pepys!" gasped Bernard Megger, swallowing between the words, "I shall remember you!"
     "You will be wasting grey matter!" replied the man.

   • 2001 September 28, Thomas K. Grose, “Connect the Dots”, in Time:

     How many phone numbers are stored in your grey matter?

2. Literal brains as a general substance.

   He fell from the 5th floor. There is grey matter on the path behind his head. I'm afraid he's dead.

3. (neuroanatomy) A collection of cell bodies and (usually) dendritic connections, in contrast to white matter.

• white matter