Crossword clue: a sofa, open carriage, or the like, so constructed that the occupants sit back to back.
1 answer found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).
Possible answers
Back to back; as, to sit dos-à-dos in a dogcart; to dance dos- à-dos, or so that two dancers move forward and pass back