'Eldest' in the Bible

So it happened, when they had come, he looked at Eliab [the eldest son] and thought, “Surely the Lord’s anointed is before Him.”

And the three eldest sons of Jesse went and followed Saul to the battle: and the names of his three sons that went to the battle were Eliab the firstborn, and next unto him Abinadab, and the third Shammah.

And David was the youngest: and the three eldest followed Saul.

And Eliab his eldest brother heard when he spake unto the men; and Eliab's anger was kindled against David, and he said, Why camest thou down hither? and with whom hast thou left those few sheep in the wilderness? I know thy pride, and the naughtiness of thine heart; for thou art come down that thou mightest see the battle.

And Saul said to David, Behold my eldest daughter Merab, her will I give thee to wife; only be thou valiant for me, and fight Jehovah's battles. But Saul thought, My hand shall not be upon him, but the hand of the Philistines shall be upon him.