After Onan’s brother Er was slain by God, his father Judah told him to fulfill his duty as a brother-in-law to Tamar, by giving her offspring. However, when Onan had intercourse with Tamar, he withdrew at themoment of ejeculation – coitus interruptus – since any child born would not legally be considered his heir. He disregarded the principle of a levirate union, so God slew him.
(Genesis 38:3-10)
Dorothy Parker named her Budgerigar “Onan” – because he was always spilling his seed on the ground