flimsy vs unsound

flimsy

adj
  • Weak; ill-founded. 

  • Likely to bend or break under pressure. 

noun
  • A banknote. 

  • Skimpy underwear. 

  • A service certificate 

  • Thin typing paper used to make multiple copies. 

unsound

adj
  • Not good, unreliable. 

  • Not whole, not solid, defective. 

  • Infirm, diseased. 

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