Albert Barnes Commentary 2 Chronicles 20:2

"Then there came some that told Jehoshaphat, saying, There cometh a great multitude against thee from beyond the sea from Syria; and, behold, they are in Hazazon-tamar (the same is En-gedi)." — 2 Chronicles 20:2 (ASV)

This can be translated as, “from beyond the sea, from Edom.” The “sea” intended is, of course, the Dead Sea. The reference to “Syria” (Aram) is probably a copyist’s error for “Edom” (compare 2 Samuel 8:12 and the note on that verse).

Regarding Engedi, see the note on 1 Samuel 23:29.