From Old Latin dū̆smus (“thickety”, adjective), a form attributed to Livius Andronicus and translated as dūmosus by Paul the Deacon's epitome of Festus. Further etymology uncertain; De Vaan and Schrijver cite Old Irish dos (“tree, bush, thicket”) as a likely cognate, from which a common stem *dus- can be reconstructed. Other possible cogates include Middle High German zūsach (“thicket”).