Dumah

(1.) silence, [comp. (Ps 94:17 )], the fourth son of Ishmael; also the tribe descended from him; and hence also the region in Arabia which they inhabited (Gen 25:14; 1Chr 1:30).

(2.) There was also a town of this name in Judah (Josh 15:52), which has been identified with ed-Domeh, about 10 miles southwest of Hebron. The place mentioned in the "burden" of the prophet Isaiah (Isa 21:11 ) is Edom or Idumea.

EBD - Easton's Bible Dictionary