The Collaborative International Dictionary of English v.0.48:

Uncia \Un"ci*a\, n.; pl. Unciae. [L. See Ounce a measure of
   weight.]
   1. (Rom. Antiq.) A twelfth part, as of the Roman as; an
      ounce.
      [1913 Webster]

   2. (Alg.) A numerical coefficient in any particular case of
      the binomial theorem. [Obs.]
      [1913 Webster]