Albert Barnes Commentary Jeremiah 38:7

"Now when Ebed-melech the Ethiopian, a eunuch, who was in the king`s house, heard that they had put Jeremiah in the dungeon (the king then sitting in the gate of Benjamin,)" — Jeremiah 38:7 (ASV)

Ebed-melech - that is, the king’s slave. By “Ethiopian” or Cushite is meant the Cushite of Africa, or negro. It seems (compare 2 Kings 23:11) that such eunuchs (or, chamberlains) took their names from the king, while the royal family and the princes generally bore names compounded with the appellations of the Deity.