The Collaborative International Dictionary of English v.0.48:

Debouch \De*bouch"\, v. i. [imp. & p. p. Debouched; p. pr. &
   vb. n. Debouching.] [F. d['e]boucher; pref. d['e]- (L. dis-
   or de) + boucher to stop up, fr. bouche mouth, fr. L. bucca
   the cheek. Cf. Disembogue.]
   To march out from a wood, defile, or other confined spot,
   into open ground; to issue.
   [1913 Webster]

         Battalions debouching on the plain.      --Prescott.
   [1913 Webster]

   2. (Geog.) To issue; -- said of a stream passing from a gorge
      out into an open valley or a plain.
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

debouch
    v 1: march out (as from a defile) into open ground; "The
         regiments debouched from the valley" [syn: debouch,
         march out]
    2: pass out or emerge; especially of rivers; "The tributary
       debouched into the big river"

Moby Thesaurus II by Grady Ward, 1.0:

58 Moby Thesaurus words for "debouch":
   arise, bail out, blow out, bob up, break cover, break forth,
   break out, break through, burst forth, cast forth, come,
   come forth, come out, decant, discharge, disembogue, disgorge,
   effuse, ejaculate, emanate, emerge, eruct, erupt, exhaust, exit,
   expel, extravasate, extrude, find vent, flare up, flash, gleam,
   irrupt, issue, issue forth, jet, jump out, leak out, ooze out,
   outpour, pop up, pour, pour forth, pour out, protrude, run out,
   sally, sally forth, send forth, send out, spew, spout, spring up,
   spurt, squirt, start up, surface, throw out