Neb'ule noun [ Confer French nébule . See nebula .] A little cloud; a cloud. [ Obsolete] « O light without nebule .» Old Ballad. Found on http://www.encyclo.co.uk/webster/N/8
In heraldry, the term nebule describes an heraldic line bounding an ordinary or subordinary, and composed of successive short curves supposed to resemble a cloud. Found on http://www.probertencyclopaedia.com/browse/UN.HTM