helmet vs top hat

helmet

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

  • 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 glans penis. 

  • 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. 

top hat

noun
  • A kind of steel batten. 

  • A man's formal hat, with a tall cylindrical crown (often of silk). 

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