Onan was a figure detailed in the Book of Genesis chapter 38, as the second son of Judah who married the daughter of Shuah the Canaanite. Onan had an older brother Er and a younger brother, Shelah as well. After being commanded by his father, Judah, to perform his duty as a husband’s brother according to the custom of levirate marriage with the late Er’s wife Tamar, Onan instead refused to perform his duty as a levirate and “spilled his seed on the ground whenever he went in” because “the offspring would not be his”, and was thus put to death by Yahweh. This act is detailed as retribution for being “displeasing in the sight of Lord”. Onan’s crime is often misinterpreted to be masturbation but it is universally agreed among biblical scholars that Onan’s death is attributed to his refusal to fulfill his obligation of levirate marriage with Tamar by committing coitus interruptus.
Or refusing to impregnate your dead brother’s widow.
https://en.wikipedia.org/wiki/Onan