rill

from WordNet (r) 3.0 (2006)

rill
    n 1: a small stream [syn: {rivulet}, {rill}, {run}, {runnel},
         {streamlet}]
    2: a small channel (as one formed by soil erosion)

from The Collaborative International Dictionary of English v.0.48

Rill \Rill\ (r[i^]l), n. [Cf. LG. rille a small channel or
   brook, a furrow, a chamfer, OE. rigol a small brook, F.
   rigole a trench or furrow for water, W. rhill a row, rhigol a
   little ditch. [root]11.]
   1. A very small brook; a streamlet.
      [1913 Webster]

   2. (Astron.) See {Rille}.
      [1913 Webster]

from The Collaborative International Dictionary of English v.0.48

Rill \Rill\, v. i.
   To run a small stream. [R.] --Prior.
   [1913 Webster]