Cul-de-sac \Cul`-de-sac"\ (ku`de-s?k" or kul`de-s?k"), n.; pl. {Culs-de-sac} (ku`- or kulz`-). [ F., lit., bottom of a bag.] 1. A passage with only one outlet, as a street closed at one end; a blind alley; hence, a trap. 2. (Mil.) a position in which an army finds itself with no way of exit but to the front. 3. (Anat.) Any bag-shaped or tubular cavity, vessel, or organ, open only at one end.