damp vs keep under

damp

verb
  • To suppress vibrations (mechanical) or oscillations (electrical) by converting energy to heat (or some other form of energy). 

adj
  • In a state between dry and wet; moderately wet; moist. 

  • Despondent; dispirited, downcast. 

noun
  • A gaseous product, formed in coal mines, old wells, pits, etc. 

  • Moisture; humidity; dampness. 

keep under

verb
  • To hold in subjection; hence, to oppress. 

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