ONAN (ō'năn, Heb. ’ônān, strong). Second son of Judah by a Canaanite wife who was a daughter of Shua. He refused to consummate a levirate marriage with Tamar, widow of his elder brother Er, who had been wicked, and so the Lord put him to death also, leaving Tamar twice a widow (Gen.38.4-Gen.38.10).

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ONAN ō’ nən (אוֹנָן, strong). The second son born to Judah and a Canaanitess named Shua. After the death of his older brother Er, whom the Lord slew for his wickedness, Onan, commanded by his father Judah to enter into a levirate marriage with his brother’s wife Tamar, failed to consummate the union. For this sin the Lord punished him with death (Gen 38:1-11). Onan’s name is mentioned also in Genesis 46:12; Numbers 26:19; 1 Chronicles 2:3.

International Standard Bible Encyclopedia (1915)

(’onan, "vigorous"; compare ONAM, a "son" of Judah (Ge 38:4,8-10; 46:12; Nu 26:19; 1Ch 2:3); "The story of the untimely death of Er and Onan implies that two of the ancient clans of Judah early disappeared" (Curtis, Chron, 84). See Skinner, Gen, 452, where it is pointed out that in Ge 38:11 Judah plainly attributes the death of his sons in some way to Tamar herself. The name is allied to Onam.