Easton's Bible Dictionary (1897)
Middle land, the third “son” of Japheth (Gen. 10:2), the name by which the Medes are known on the Assyrian monuments.
Smith's Bible Dictionary (1863)
(middle land), (Genesis 10:2) is usually called the third son of Japhet, and the progenitor of the Medes; but probably all that is intended is that the Medes, as well as the Gomerites, Greeks, Tabareni, Moschi, etc., descended from Japhet.
Hastings' Dictionary of the Bible (1898) & Schaff's Bible Dictionary
MAD'AI (middle land), the third son of Japheth, from whom the Medes descended. Gen 10:2; 1 Chr 1:5.
Hitchcock's Bible Names (1869)
a measure; judging; a garment