plug away at vs wade

plug away at

wade

noun
  • An act of wading. 

  • A ford; a place to cross a river. 

verb
  • To enter recklessly. 

  • to progress with difficulty 

  • to walk through (water or similar impediment); to pass through by wading 

  • to walk through water or something that impedes progress. 

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