'Son in law' in the Bible

Then David responded, “Who am I, and what is my family or my father’s clan in Israel that I should become the king’s son-in-law?”

“I’ll give her to him,” Saul thought. “She’ll be a trap for him, and the hand of the Philistines will be against him.” So Saul said to David a second time, “You can now be my son-in-law.”

Saul then ordered his servants, “Speak to David in private and tell him, ‘Look, the king is pleased with you, and all his servants love you. Therefore, you should become the king’s son-in-law.’”

Saul’s servants reported these words directly to David, but he replied, “Is it trivial in your sight to become the king’s son-in-law? I am a poor man who is common.”

When the servants reported these terms to David, he was pleased to become the king’s son-in-law. Before the wedding day arrived,

David and his men went out and killed 200 Philistines. He brought their foreskins and presented them as full payment to the king to become his son-in-law. Then Saul gave his daughter Michal to David as his wife.

Ahimelech replied to the king: “Who among all your servants is as faithful as David? He is the king’s son-in-law, captain of your bodyguard, and honored in your house.