Source : Webster's Revised Unabridged Dictionary (1913)

Bayou \Bay"ou\, n.; pl. {Bayous}. [North Am. Indian bayuk, in F.
   spelling bayouc, bayouque.]
   An inlet from the Gulf of Mexico, from a lake, or from a
   large river, sometimes sluggish, sometimes without
   perceptible movement except from tide and wind. [Southern U.
   S.]

         A dark slender thread of a bayou moves loiteringly
         northeastward into a swamp of huge cypresses. --G. W.
                                                  Cable.

Source : WordNet®

bayou
     n : a swampy arm or slow-moving outlet of a lake (term used
         mainly in Mississippi and Louisiana)