foster vs spark off

foster

verb
  • To cultivate and grow something. 

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

  • To nurse or cherish something. 

adj
  • Related by such care. 

  • Receiving such care. 

  • Providing parental care to children not related to oneself. 

noun
  • A foster parent. 

  • The care given to another; guardianship. 

spark off

verb
  • To initiate something by providing the necessary conditions. 

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