riv·u·let 
(rĭvyə-lĭt)
(rĭvyə-lĭt)n.
A small brook or stream; a streamlet.
[Possibly from Italian rivoletto, diminutive of rivolo, small stream, from Latin rīvulus, diminutive of rīvus, stream; see rei- in the Appendix of Indo-European roots.]