WEB
Onan knew that the seed wouldn’t be his; and it happened, when he went in to his brother’s wife, that he spilled it on the ground, lest he should give seed to his brother.
YLT
and Onan knoweth that the seed is not reckoned his; and it hath come to pass, if he hath gone in unto his brother’s wife, that he hath destroyed it to the earth, so as not to give seed to his brother;