New Defender's Study Bible Notes
20:2 my sister. How Abraham and Sarah could have entered into the same type of deception for which they had long before been rebuked in Egypt (Genesis 12:10-20) is hard to understand, but apparently the situation took them by surprise and they got trapped into the same old subterfuge before they realized it.
20:2 Abimelech. Abimelech was evidently a title, like Pharaoh in Egypt. Gerar was a prosperous Philistine settlement along the coast, near the Egyptian border, and Abraham must have journeyed there for business purposes.