worker vs workhorse

worker

noun
  • A person who performs labor for a living, especially manual labor. 

  • A nonreproductive social insect, such as ant, bee, termite, or wasp. 

  • A female ant, bee, termite or wasp. 

  • A thread performing one instance of a particular task within a program. 

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