on thin ice vs perilous

on thin ice

adv

  • dangerously, hazardously, delicately 

prep

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

perilous

adj

  • Dangerous, full of peril. 

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