tributary vs underaverage

tributary

adj
  • subordinate; inferior 

  • Related to the paying of tribute. 

  • Yielding supplies of any kind; serving to form or make up, a greater object of the same kind, as a part, branch, etc.; contributing. 

noun
  • A nation, state, or other entity that pays tribute. 

  • A natural water stream that flows into a larger river or other body of water. 

  • A vein which drains into a another vein. 

underaverage

adj
  • Below average. 

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