hardhead vs rainbow trout

hardhead

noun
  • Any of certain saltwater sciaenid (Sciaenidae) fishes. 

  • Any of several weeds in or formerly classified in the genus Centaurea, particularly Russian knapweed (Acroptilon repens). 

  • A Scottish billon coin circulated in the reigns of Mary and James VI. 

  • Residual ore that failed to melt during a smelting process. 

  • One who is practical or hardheaded. 

  • A brown diving duck, Aythya australis, native to Australia. 

  • Mylopharodon conocephalus of fresh waters in California. 

rainbow trout

noun
  • The fish as food. 

  • A trout of the species Oncorhynchus mykiss, that has black spots and a pink streak running along the body. 

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