Onanism
Origin
From the biblical name Onan: In the Book of Genesis, Onan, son of Judah, in fulfillment of the laws of levirate marriage was to impregnate his brother Er's widow, Tamar, in order to raise offspring from the union in his brother's name. In order to avoid raising descendants for his late brother, however, Onan spilled his semen on the ground when he went in to his brother's wife, so that he would not give offspring to his brother. (Genesis 38:9). Thus the word Onanism was coined, meaning ejaculating outside the vagina, or masturbation (because this also spills semen, rather than using it for procreation).
Full definition of onanism
Noun
onanism
(usually uncountable; plural onanisms)- ejaculating outside the vagina during intercourse; (the performing of) coitus interruptus
- masturbation