reversion vs underside

reversion

noun
  • The action of turning something the reverse way. 

  • The action of reverting something. 

  • The return of a genetic characteristic after a period of suppression. 

  • The fact of being turned the reverse way. 

  • The right of succeeding to an estate, or to another possession. 

  • The act of conversion to Islam, due to the belief that all people are born Muslim. 

  • The return of an estate to the donor or grantor after expiry of the grant. 

  • The action of returning to a former condition or practice. 

  • A sum payable on a person's death. 

  • The right of succeeding to an office after the death or retirement of the holder. 

  • An estate which has been returned in this manner. 

underside

noun
  • The side that is below or underneath, the bottom. 

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