implement vs subserve

implement

verb
  • To bring about; to put into practice; to carry out. 

noun
  • A tool or instrument for working with. 

subserve

verb
  • To assist in carrying out. 

  • To serve to promote (an end); to be useful to. 

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