servant vs workhorse

servant

noun
  • One who is hired to perform regular household or other duties, and receives compensation. As opposed to a slave. 

  • A person of low condition or spirit. 

  • One who serves another, providing help in some manner. 

  • A person who dedicates themselves to God. 

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 servant and workhorse occurred in a corpus of books? (source: Google Ngram Viewer )