ozone vs undercurrent

ozone

noun
  • Fresh air, especially that breathed at the seaside and smelling of seaweed. 

  • An allotrope of oxygen (symbol O₃) having three atoms in the molecule instead of the usual two; it is a toxic gas, generated from oxygen by electrical discharge. 

  • Hypernym: greenhouse gas 

verb
  • To treat with ozone. 

undercurrent

noun
  • A tendency of feeling or opinion that is concealed rather than exposed. 

  • A current of water which flows under the surface, and often in a different direction from surface currents. 

verb
  • To flow under some surface. 

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