fee vs obligate

fee

verb
  • To reward for services performed, or to be performed; to recompense; to hire or keep in hire; hence, to bribe. 

noun
  • A right to the use of a superior's land as a stipend for certain services to be performed, typically military service. 

  • An additional monetary payment charged for a service or good that is minor compared to the underlying cost. 

  • Synonym of fief: the land so held. 

  • An inheritable estate in land, whether absolute and without limitation to potential heirs (fee simple) or with limitations to particular kinds of heirs (fee tail). 

  • An inheritable estate in land held of a feudal lord on condition of performance of certain services, typically military service. 

obligate

verb
  • To cause to be grateful or indebted; to oblige. 

  • To bind, compel, constrain, or oblige by a social, legal, or moral tie. 

  • To commit (money, for example) in order to fulfill an obligation. 

adj
  • Requiring a (specified) way of life, habitat, etc.. 

  • Indispensable; essential; necessary; obligatory; mandatory; unavoidably invoked. 

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