Genesis 38:9

⁹ And Onan knew that the seed would not be his: and it came to pass, when he went in to his brother's wife, that he frustrated the purpose, lest he should give seed to his brother.

Belly

The belly, in Psalms 16:4, signifies the interior understanding.

In Genesis 25:23, it signifies conception of interior and exterior good. (Arcana Coelestia 3293)

In Isaiah 46:3, the belly signifies from the beginning of the church. (Arcana Coelestia 4918[2], 5550)

The belly signifies people who are being regenerated, and people who have been regenerated. (Apocalypse Explained 710[3])