obligatory vs servile

obligatory

adj
  • Requiring a matter or obligation. 

  • Imposing obligation, legally, morally, or otherwise; binding; mandatory. 

servile

adj
  • Of or pertaining to a slave. 

  • Not belonging to the original root. 

  • Slavish or submissive. 

  • Not sounded, but serving to lengthen the preceding vowel, like the e in tune. 

noun
  • A slave; a menial. 

  • An element which forms no part of the original root. 

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