The Collaborative International Dictionary of English v.0.48:

dilly \dil"ly\ (d[i^]l"l[y^]), n. [Contr. fr. diligence.]
   A kind of stagecoach. "The Derby dilly." --J. H. Frere.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

dilly \dil"ly\ (d[i^]l"l[y^]), n.
   something remarkable, highly unusual, or exceptionally
   effective; as, a dilly of a movie; when I make a mistake,
   it's a dilly.
   [PJC]

Moby Thesaurus II by Grady Ward, 1.0:

39 Moby Thesaurus words for "dilly":
   absurd, ace, balmy, beaut, corker, crackerjack, crazy, daisy,
   dally, dandy, darb, dillydally, dream, harebrained, honey,
   humdinger, insane, killer-diller, knockout, lag, linger, loiter,
   lollapaloosa, loony, lulu, nifty, peach, pip, pippin, poke, potty,
   put off, rouser, silly, sweetheart, tarry, the nuts, wacky, whiz