Patronymically from an unused name from shuwm probably meaning garlic-smell; a Shumathite (collectively) or descendants of Shumah -- Shumathites.
see HEBREW shuwm
H8126. Shumathi
[שֻׁמָה] proper name, masculine whence
שֻׁמָתִי adjective, of a people in Caleb, with article as collective noun ׳הַשּׁ 1 Chronicles 2:53; Ησαμαθειμ[ν], δ Σαμαθι.
שׁמה (apparently √ of following; Sta§324 a.; so Thes, compare Arabic be high, lofty (or is this secondary?); JenKosmol. (1890), 6 compare Assyrian šamû, id. (>šamû = sparkle, IdZK ii (1885), 53); compare DlWB).