Genesis 38:4

And she conceived again, and bare a son,.... As soon as she well could:

and she called his name Onan; the first son Judah gave the name to, but his wife named this, so called from grief or sorrow; the reason of it, according to the above Targum, was,

"because his father would mourn for him;''

he was a Benoni, see Genesis 35:18, whose sin and immature death caused sorrow.