commutation vs quid pro quo

commutation

noun
  • Substitution of one thing for another; interchange. 

  • The reversal of an electric current. 

  • The change to a lesser penalty or punishment by the State 

  • Substitution, as a means of discriminating between phonemes. 

  • The process or habit of journeying to and from work on a regular basis; commuting. 

  • Specifically, the substitution of one kind of payment for another, especially a switch to monetary payment from obligations of labour. 

quid pro quo

noun
  • Substitution of one drug for another. 

  • An equal or fair transaction or series of process of exchange transactions; tit for tat. 

  • Something which is offered or asked for in exchange for something else. 

  • Something which is understood as something else; an equivocation. 

  • A usually non-monetary exchange transaction, or series or process of exchange transactions. 

  • Sexual harassment in which a person in a workplace implicitly or explicitly requires sexual favours in exchange for something. 

How often have the words commutation and quid pro quo occurred in a corpus of books? (source: Google Ngram Viewer )