onan·ism \ˈōnəˌnizəm\noun (-s) Etymology: probably from (assumed) New Latin onanismus, from Onan, son of Judah described in Gen 38: 9 as practicing coitus interruptus + Latin -ismus -ism 1.: coitus interruptus 2.: masturbation 3.: self-gratification < the kind of intellectual onanism to which he was dedicated — Esther P. Shiverick > • onan·is·tic\|ōnə|nistik\adjective