The Collaborative International Dictionary of English v.0.48:

Tubule \Tu"bule\, n. [F. tubule, or L. tubulus, dim. of tubus a
   tube, a pipe.]
   1. A small pipe or fistular body; a little tube.
      [1913 Webster]

   2. (Anat.) A minute tube lined with glandular epithelium; as,
      the uriniferous tubules of the kidney.
      [1913 Webster]

WordNet (r) 3.0 (2006):

tubule
    n 1: a small tube