plug away vs slave

plug away

verb
  • To persist or continue, as with an effort. 

slave

verb
  • To work hard. 

  • To work as a slaver, to enslave people. 

  • To place a device under the control of another. 

noun
  • A sex slave, a person who is forced against their will to perform, for another person or group, sexual acts on a regular or continuing basis. 

  • An abject person. 

  • A submissive partner in a BDSM relationship who (consensually) submits to (sexually and/or personally) serving one or more masters or mistresses. 

  • A device (such as a secondary flash or hard drive) that is subject to the control of another (a master). 

  • A person who is held in servitude as the property of another person, and whose labor (and often also whose body and life) is subject to the owner's volition and control. 

  • A drudge; one who labors or is obliged (e.g. by prior contract) to labor like a slave with limited rights, e.g. an indentured servant. 

  • One who has no power of resistance (to something), one who surrenders to or is under the domination (of something). 

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