The Collaborative International Dictionary of English v.0.48:

Venule \Ven"ule\ (v[e^]n"[-u]l), n. [L. venula, dim. from vena
   vein.]
   A small vein; a veinlet; specifically (Zool.), one of the
   small branches of the veins of the wings in insects.
   [1913 Webster]

WordNet (r) 3.0 (2006):

venule
    n 1: a minute vein continuous with a capillary [syn: venule,
         venula, capillary vein]