Then to Sarah he said, “Behold, I have given your brother a thousand pieces of silver; indeed this vindicates you before all who are with you and before everybody.” Thus she was rebuked.
Genesis 20:16 (NKJV)
The Hebrew phrase that is translated as "this vindicates you" here is כְּסוּת עֵינַיִם, which means "a covering of the eyes."
The meaning is debated among the rabbis, but Chizkuni's interpretation seems to be the best.
There is sarcasm in the words.
Per tradition, it is proper to give a great gift to the brother of a bride. In Genesis 24:53, we read Eliazar gave precious gifts to Rebecca's brother and her mother.
So Abimelech's statement, "your brother," is meant to nod to the tradition, even though he knows it's not true.
In that context, "a covering of the eyes" is like "turning a blind eye."
The word "rebuked" at the end is also difficult to translate, as it can mean both "rebuked" but also "cleared" or "shown to be right." Perhaps it's both, as the matter is dropped after Abraham prays for healing.