knucklehead vs loggerhead

knucklehead

noun
  • An idiot; a stupid or inept person. 

loggerhead

noun
  • The loggerhead duck or Falkland steamer duck (Tachyeres brachypterus; formerly Tachyeres cinereus), a species of steamer duck endemic to the Falkland Islands. 

  • The loggerhead kingbird (Tyrannus caudifasciatus), a bird endemic to the Caribbean and West Indies. 

  • The loggerhead sea turtle or loggerhead turtle (Caretta caretta), an oceanic turtle found throughout the world. 

  • A thistle-like flowering plant of the genus Centaurea, particularly the common knapweed (Centaurea nigra). 

  • The loggerhead musk turtle (Sternotherus minor), a large-headed turtle endemic to the United States. 

  • A metal tool consisting of a long rod with a bulbous end that is made hot in a fire, then plunged into some material (such as pitch or a liquid) to melt or heat it. 

  • The loggerhead shrike (Lanius ludovicianus), a bird endemic to North America. 

  • The rufous-tailed flycatcher (Myiarchus validus), a bird endemic to Jamaica. 

  • A post on a whaling boat used to secure the harpoon rope. 

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