foster vs hold onto

foster

verb
  • To nurse or cherish something. 

  • To cultivate and grow something. 

  • To nurture or bring up offspring, or to provide similar parental care to an unrelated child. 

noun
  • A foster parent. 

  • The care given to another; guardianship. 

adj
  • Related by such care. 

  • Receiving such care. 

  • Providing parental care to children not related to oneself. 

hold onto

verb
  • To manage to keep something. 

  • Used other than figuratively or idiomatically: see hold, onto. 

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