grey matter

(British & Australian humorous) also gray matter (American humorous)

your intelligence It's an entertaining film but it doesn't exactly stimulate the old grey matter.

Name	Pronounced	Usage
Photine	-	Ancient Greek
Chrysanta	kri-SAN-tə	English (Rare)
JerÓNimo	he-RO-nee-mo (Spanish)	Spanish, Portuguese
Feidhelm	-	Irish
Cajetan	-	History
Liat	-	Hebrew