The Collaborative International Dictionary of English v.0.48:

Fractional \Frac"tion*al\, a.
   1. Of or pertaining to fractions or a fraction; constituting
      a fraction; as, fractional numbers.
      [1913 Webster]

   2. Relatively small; inconsiderable; insignificant; as, a
      fractional part of the population.
      [1913 Webster]

   Fractional crystallization (Chem.), a process of gradual
      and approximate purification and separation, by means of
      repeated solution and crystallization therefrom.

   Fractional currency, small coin, or paper notes, in
      circulation, of less value than the monetary unit.

   Fractional distillation (Chem.), a process of distillation
      so conducted that a mixture of liquids, differing
      considerably from each other in their boiling points, can
      be separated into its constituents.
      [1913 Webster]

WordNet (r) 3.0 (2006):

fractional currency
    n 1: paper currency in denominations less than the basic
         monetary unit