helmet vs skull

helmet

noun
  • A hard, protective head covering, typically part of armour. 

  • The hood-shaped upper sepal or petal of some flowers, as of the monkshood or the snapdragon. 

  • A naked shield or protuberance on the top or fore part of the head of a bird. 

  • The feature above a shield on a coat of arms. 

  • The glans penis. 

  • A contemptible or stupid person. 

  • The upper part of a chemist's retort. 

verb
  • To cover with, or as if with, a helmet. 

skull

noun
  • The crown of the headpiece in armour. 

  • A crust formed on the ladle, etc. by the partial cooling of molten metal. 

  • The mind or brain. 

  • A shallow bow-handled basket. 

  • The main bones of the head considered as a unit; including the cranium, facial bones, and mandible. 

  • These bones as a symbol for death; death's-head. 

verb
  • To strike the top of (the ball). 

  • To hit in the head with a fist, a weapon, or a thrown object. 

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