noun

• (geography) A narrow outlet from which a body of water pours.
  "In level portions of the country vertical shafts are preferred, but where the mine is situated upon a hill a debouch may often be found below the sulphur seam, ..."
• (military) A fortress at the end of a defile.
  "To prevent another demonstration of this character, and to insure a debouch on the south bank of the James, it became necessary to occupy Coggin's Point, which was done on the 3d, and the enemy driven back towards Petersburg."

verb

• (intransitive) To pour forth from a narrow opening; to emerge from a narrow place like a defile into open country or a wider space.
  "The pretty pimpled young man, no longer a boy, came down from the imperial box in his purple to the performers’ well which debouched into the arena."