onanism vs self-pleasure

onanism

noun

  • Masturbation. 

  • Ejaculating outside the vagina during intercourse; (the performing of) coitus interruptus. 

self-pleasure

noun

  • masturbation 

verb

  • To pleasure oneself; masturbate. 

How often have the words onanism and self-pleasure occurred in a corpus of books? (source: Google Ngram Viewer )