lackey vs workhorse

lackey

noun
  • A footman, a liveried male servant. 

  • A fawning, servile follower. 

verb
  • To attend, wait upon, serve obsequiously. 

workhorse

noun
  • Anyone or anything that does a lot of work; something or someone who works consistently or regularly. 

  • A horse used primarily for manual labor; a draft horse. 

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