grey matter

English

grey matter (uncountable)

(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 Sep. 28, Thomas K. Grose, "Connect the Dots," Time:
  How many phone numbers are stored in your grey matter?
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."
(neuroanatomy) A collection of cell bodies and (usually) dendritic connections, in contrast to white matter.

person's ability to think

collection of cell bodies