buck up vs undermine

buck up

verb
  • To pass on to higher authority for resolution. See also pass the buck. 

  • To encourage; to hearten. 

  • To become encouraged, reinvigorated, or cheerful; to summon one's courage or spirits; to pluck up courage. 

intj
  • Cheer up; take courage; take heart. 

undermine

verb
  • To weaken or work against; to hinder, sabotage. 

  • To erode the base or foundation of something, e.g. by the action of water. 

  • To dig underneath (something), to make a passage for destructive or military purposes; to sap. 

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