bonnet vs helmet

bonnet

noun
  • The polishing head of a power buffer, often made of wool. 

  • A metallic canopy, or projection, over an opening, as a fireplace, or a cowl or hood to increase the draught of a chimney, etc. 

  • The second stomach of a ruminant. 

  • A ducat, an old Scottish coin worth 40 shillings. 

  • A roofing over the cage of a mine, to protect its occupants from objects falling down the shaft. 

  • A traditional Scottish woollen brimless cap; a bunnet. 

  • A small defence work at a salient angle; or a part of a parapet elevated to screen the other part from enfilade fire. 

  • A frame of wire netting over a locomotive chimney, to prevent escape of sparks. 

  • In pumps, a metal covering for the openings in the valve chambers. 

  • A mushroom of the genus Mycena. 

  • A type of hat, once worn by women or children, held in place by ribbons tied under the chin. 

  • The hinged cover over the engine of a motor car; a hood. 

  • A length of canvas attached to a fore-and-aft sail to increase the pulling power. 

verb
  • To put a bonnet on. 

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. 

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