Lightly Here, means perhaps. The heathen considered fornication either as no sin, or a very little one; but they had a different idea of adultery, considering it as heinous. Therefore, with a reference to it, Abimelech says, Thou shouldest have brought guiltiness upon us Probably it might be fresh in his memory how sorely God had punished his predecessor and all his family in the days of Abraham (chap. 20.) for only an intention of adultery. It is very observable here, that Abimelech takes it for granted, that their ignorance of Rebekah's being Isaac's wife would not have been a sufficient excuse for their sin.
Related Commentaries of Genesis 26:10
Genesis 26:10
10 And Abimelech said, What is this thou hast done unto us? one of the people might lightly have lien with thy wife, and thou shouldest have brought guiltiness upon us.