helmet vs warhead

helmet

noun
  • The glans penis. 

  • 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. 

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

  • A contemptible or stupid person. 

  • The upper part of a chemist's retort. 

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

warhead

noun
  • The glans penis. 

  • The part of a missile, projectile, torpedo, rocket, or other munition which contains either the nuclear or thermonuclear system, high explosive system, chemical or biological agents, or inert materials intended to inflict damage. 

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