From BiblePortal Wikipedia

Smith's Bible Dictionary [1]

Leum'mim. (Peoples). The name of the third, of the descendants of Dedan, son of Jokshan,  Genesis 25:3, being in the plural form, like his brethren, Asshurim and Letushim.

Hastings' Dictionary of the Bible [2]

Leummim A tribe of the Dedanites (  Genesis 25:3 ). Cf. Letushim.

Morrish Bible Dictionary [3]

Son of Dedan, a son of Jokshan.  Genesis 25:3 .

Fausset's Bible Dictionary [4]

 Genesis 25:3. A tribe, ("the peoples").

Holman Bible Dictionary [5]

 1 Chronicles 1:32

Easton's Bible Dictionary [6]

 Genesis 25:3

Cyclopedia of Biblical, Theological and Ecclesiastical Literature [7]

(Heb. Leiimmimn', לְאֻמַּים , Peoples, as often; Sept. Λαωμείμ ) , the last named of the three sons of Dedan (grandson of Abraham by Keturah), and head of an Arabian tribe descended from him ( Genesis 25:3; and Vulgate at  1 Chronicles 1:32). B.C. considerably post 2024. (See Arabia).

They are supposed to be the same with the Allumoeotoe ( Ἀλλουμαιῶται ) , named by Ptolemy (6: 7, 24) as near the Gerrhaei, which appears to be a corruption of the Hebrew word with the art. prefixed. He also enumerates Luma among the towns of Arabia Deserta (5:19), and Forster ( Geogr. Of Arabia, 1:335) suggests that this may liave been an ancient settlement of the same tribe" (Kitto). "They are identified by Fresnel (in the Journ. Asiat. iiie serie, 6:217) with an Arab tribe called Umeiyim, one of the very ancient tribes of Arabia of which no genealogy is given by the Arabs, and who appear to have been ante-Abrahamic, and possibly aboriginal inhabitants of the country." (See Letushim).

International Standard Bible Encyclopedia [8]

lḗ - um´im ( לאמּים , le'ummı̄m ): A D edanite tribe of North Arabia, connected with the Letushim (which see).