The Collaborative International Dictionary of English v.0.48:

Ratable \Rat"a*ble\ (r[=a]t"[.a]*b'l), a.
   1. Capable of being rated, or set at a certain value.
      [1913 Webster]

            Twenty orae were ratable to [at] two marks of
            silver.                               --Camden.
      [1913 Webster]

   2. Liable to, or subjected by law to, taxation; as, ratable
      estate.
      [1913 Webster]

   3. Made at a proportionate rate; as, ratable payments. --
      Rat"a*ble*ness, n. -- Rat"a*bly, adv.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

ratable \rat"a*ble\ (r[=a]t"[.a]*b'l), n.
   a structure which may be rated, or set at a certain value,
   for the purpose of taxation, usually based on the value; as,
   with the deterioration of the center cities, the loss of
   ratables worsened the situation by removing valuable sources
   of tax revenue.
   [PJC]

WordNet (r) 3.0 (2006):

ratable
    adj 1: liable to payment of locally assessed property taxes;
           "the ratable value of property" [syn: ratable,
           rateable]