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]

Moby Thesaurus II by Grady Ward, 1.0:

38 Moby Thesaurus words for "ratable":
   assessable, assessment, cess, chargeable, conscience money,
   contribution, direct tax, dutiable, duty, graduated taxation,
   imposition, impost, indirect tax, joint return, leviable, levy,
   progressive tax, separate returns, single tax, supertax, surtax,
   tax, tax base, tax dodging, tax evasion, tax exemption, tax return,
   tax structure, tax withholding, tax-exempt status, taxable,
   taxable income, taxation, tithable, tithe, toll, tribute,
   withholding tax