Source : Webster's Revised Unabridged Dictionary (1913)

Nullah \Nul"lah\, n. [Hind. n[=a]l[=a], fr. Skr. n[=a]la tube.]
   A water course, esp. a dry one; a gully; a gorge; -- orig. an
   East Indian term. --E. Arnold.

Source : WordNet®

nullah
     n : a ravine or gully in southern Asia