skullcap vs watch cap

skullcap

noun
  • A small domed cap that covers the area from the forehead to just above the back of the neck. 

  • A yarmulke-like hat worn as an element of ghetto fashion. 

  • The calvaria, the top part of the skull, covering the cranial cavity containing the brain. 

  • Any of several species of flowering plants of the genus Scutellaria, in the Lamiaceae family. 

  • A torture device for compressing the skull. 

watch cap

noun
  • A knitted cap, such as the one worn by a seaman when on watch. 

How often have the words skullcap and watch cap occurred in a corpus of books? (source: Google Ngram Viewer )