skullcap

Short definition from Wiktionary

Noun

1. 1
   A small domed cap that covers the area from the forehead to just above the back of the neck.
2. 2
   A yarmulke-like hat.
3. 3
   The calvaria, the top part of the skull, covering the cranial cavity containing the brain.
4. 4
   Any of several species of flowering plants of the genus Scutellaria, in the Lamiaceae family.
5. 5
   A torture device for compressing the skull.