Albert Barnes Commentary 1 Kings 2:39

"And it came to pass at the end of three years, that two of the servants of Shimei ran away unto Achish, son of Maacah, king of Gath. And they told Shimei, saying, Behold, thy servants are in Gath." — 1 Kings 2:39 (ASV)

Achish - This is possibly the Achish mentioned in the marginal reference, but more likely the grandson of the former Achish.