grey matter

Noun

grey matter (uncountable)

1. (idiomatic) Brains; a person's ability to think.
   • "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."1904, Lucy Maud Montgomery, “Penelope's Party Waist”, in Short Stories: 1904
   • "Inspector Pepys!" gasped Bernard Megger, swallowing between the words, "I shall remember you!"
     "You will be wasting grey matter!" replied the man.1914, Sax Rohmer, chapter 10, in The Sins of Severac Bablon
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. A collection of cell bodies and (usually) dendritic connections, in contrast to white matter.