iffy vs on thin ice

iffy

adj
  • Uncertain or chancy. 

  • Of dubious authenticity, legitimacy or legality. 

on thin ice

prep
  • In a dangerous, hazardous, or delicate situation; at risk. 

adv
  • dangerously, hazardously, delicately 

How often have the words iffy and on thin ice occurred in a corpus of books? (source: Google Ngram Viewer )