Wiktionary
dos a dos
adv. Back to back. n. 1 A move in square dancing in which two dancers face each other, then step forward and left until they have right shoulders adjacent, then move to a position where they are back to back, then move to have left shoulders adjacent, then return to facing each other. 2 (cx historical English) A sofa, open carriage, etc. constructed so that the occupants sit back to back.