brain bucket

noun2

1. •
   (humorous) A protective helmet, as worn, for example, by a motorcyclist, bicyclist, or soldier in combat.

   • The Air Force not only makes up words and phrases (e.g., brain bucket for crash helmet) . . . . — 1956
2. •
   (old-fashioned) The skull; the head.

   • [H]e fetched me such a clip on top of my brain-bucket as to drive all my senses clear down into my boots. — 1856