The Collaborative International Dictionary of English v.0.48:

Tilly-vally \Til"ly-val`ly\, interj., adv., or a.
   A word of unknown origin and signification, formerly used as
   expressive of contempt, or when anything said was rejected as
   trifling or impertinent. [Written also tille-vally,
   tilly-fally, tille-fally, and otherwise.] --Shak.
   [1913 Webster]