The Collaborative International Dictionary of English v.0.48:

nebule \neb"ule\, n. [Cf. F. n['e]bule. See nebula.]
   A little cloud; a cloud. [Obs.]
   [1913 Webster]

         O light without nebule.                  --Old Ballad.
   [1913 Webster] Nebule

The Collaborative International Dictionary of English v.0.48:

N'ebul'e \N['e]`bu`l['e]"\, Nebuly \Neb"u*ly\, a. [F.
   n['e]bul['e].] (Her.)
   Composed of successive short curves supposed to resemble a
   cloud; -- said of a heraldic line by which an ordinary or
   subordinary may be bounded.
   [1913 Webster]

WordNet (r) 3.0 (2006):

nebule
    n 1: a small cloud