O'nan (Heb. Onanz', אוֹנָן, strong; Sept. Αὐνάν), the second son of Judah by the daughter of Shuah the Canaanite (Ge 38:4; Nu 26:19; 1Ch 3:3). Being constrained by the obligations of the ancient Levirate law (q.v.) to espouse Tamar, his elder brother's widow, he took means to frustrate the intention of this usage, which was to provide heirs for a brother who had died childless (De 25:5-10; Mr 12:1-9). This offense, rendered without excuse by the allowance of polygamy, and the seriousness of which can scarcely be appreciated but in respect to the usages of the times in which it was committed, was punished by premature death (Ge 38:8 sq.). B.C. cir. 1870. His act was evidently different from the vice which has been given his name.