"rightwise, turned toward the right; motion according to the apparent course of the sun," 1771, from Gaelic deiseil, deiseal (adjective and adverb) "toward the south," taken in sense of "toward the right," from deas "right, right-hand; south," cognate with Irish deas, Old Irish dess, des, Welsh dehau, and ultimately with Latin dexter (see dexterity). The second element of the Gaelic word is not explained (one old guess, in the Century Dictionary (1902), is a proposed *iul "direction, guidance").