cling to vs hang onto

cling to

verb
  • To remain by (someone's) side; to refuse to leave the company of. 

  • To have an intense emotional dependency on (someone). 

  • Used other than figuratively or idiomatically: see cling, to. 

hang onto

verb
  • to keep 

How often have the words cling to and hang onto occurred in a corpus of books? (source: Google Ngram Viewer )