soft-soap vs suasion

soft-soap

noun

  • Persuasion by means of flattery or pleasing words. 

verb

  • To attempt to persuade by flattery or pleasing words; to butter up. 

suasion

noun

  • The act of urging or influencing; persuasion. 

How often have the words soft-soap and suasion occurred in a corpus of books? (source: Google Ngram Viewer )