tranquilizing vs tranquillizing

tranquilizing

noun
  • The act of calming a person or animal, or putting them to sleep, using a drug. 

  • The act of making someone or something tranquil. 

adj
  • Of a drug: having the effect of calming a person or animal, or putting them to sleep; sedating, sedative. 

  • Having the effect of making someone or something tranquil; calming, soothing. 

tranquillizing

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