'Heir' in the Bible

But Abram replied, "Lord GOD, what can you give me since I continue to be childless, and the heir of my household is Eliezer from Damascus?

Look!" Abram said, "You haven't given me any offspring, so a servant born in my house is going to be my heir."

A message came from the LORD to him again: "This one will not be your heir. Instead, the child who will be born to you will be your heir."

But Onan knew that the offspring wouldn't be his own heir, so whenever he had sexual relations with his brother's wife, he would spill his semen on the ground to avoid fathering offspring for his brother.