Synonyms for Onanism (same or very similar meaning)
WordNet sense 1 (manual stimulation of the genital organs (of yourself or another) for sexual pleasure):
masturbationWordNet sense 2 (a method of birth control in which coitus is initiated but the penis is deliberately withdrawn before ejaculation):
coitus interruptus, pulling out, withdrawal methodFrom the ODE community, based on WordNetadd/edit