principled vs slippery

principled

adj
  • Based on, having, or manifesting principles 

  • strongly adhering to, or heedful of, guiding beliefs or moral rules 

slippery

adj
  • Unstable; changeable; inconstant. 

  • Evasive; difficult to pin down. 

  • Of a surface, having low friction, often due to being covered in a non-viscous liquid, and therefore hard to grip, hard to stand on without falling, etc. 

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