The Collaborative International Dictionary of English v.0.48:

Rebate \Re*bate"\, n.
   1. Diminution.
      [1913 Webster]

   2. (Com.) Deduction; abatement; as, a rebate of interest for
      immediate payment; a rebate of importation duties.
      --Bouvier.
      [1913 Webster]

   3. A portion of a sum paid, returned to the purchaser, as a
      method of discounting. The rebate is sometimes returned by
      the manufacturer, after the full price is paid to the
      retailer by the purchaser.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

Rebate \Re*bate"\, n. [See Rabbet.]
   1. (Arch.) A rectangular longitudinal recess or groove, cut
      in the corner or edge of any body; a rabbet. See Rabbet.
      [1913 Webster]

   2. A piece of wood hafted into a long stick, and serving to
      beat out mortar. --Elmes.
      [1913 Webster]

   3. An iron tool sharpened something like a chisel, and used
      for dressing and polishing wood. --Elmes.
      [1913 Webster]

   4. [Perhaps a different word.] A kind of hard freestone used
      in making pavements. [R.] --Elmes.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Rebate \Re*bate"\ (r[-e]*b[=a]t"), v. t. [F. rebattre to beat
   again; pref. re- re- + battre to beat, L. batuere to beat,
   strike. See Abate.]
   1. To beat to obtuseness; to deprive of keenness; to blunt;
      to turn back the point of, as a lance used for exercise.
      [1913 Webster]

            But doth rebate and blunt his natural edge. --Shak.
      [1913 Webster]

   2. To deduct from; to make a discount from, as interest due,
      or customs duties. --Blount.
      [1913 Webster]

   3. To return a portion of a sum paid, as a method of
      discounting of prices.
      [PJC]

   Rebated cross, a cross which has the extremities of the
      arms bent back at right angles, as in the fylfot.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Rebate \Re*bate"\, v. t.
   To cut a rebate in. See Rabbet, v.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Rebate \Re*bate"\, v. i.
   To abate; to withdraw. [Obs.] --Foxe.
   [1913 Webster]

WordNet (r) 3.0 (2006):

rebate
    n 1: a refund of some fraction of the amount paid [syn:
         rebate, discount]
    2: a rectangular groove made to hold two pieces together [syn:
       rabbet, rebate]
    v 1: give a reduction in the price during a sale; "The store is
         rebating refrigerators this week"
    2: cut a rebate in (timber or stone)
    3: join with a rebate; "rebate the pieces of timber and stone"

Moby Thesaurus II by Grady Ward, 1.0:

57 Moby Thesaurus words for "rebate":
   abate, abatement, agio, allow, allowance, bank discount, bate,
   breakage, bribe, cash discount, chain discount, charge off,
   charge-off, commission, concession, cut, deduct, deduction,
   depreciate, depreciation, diminish, discount, drain, drawback,
   graft, kick back, kickback, make allowance, mark down, payola,
   penalty, penalty clause, percentage, premium, price reduction,
   price-cut, rake-off, rebatement, reduce, reduction, refund, repay,
   repayment, rollback, salvage, setoff, subtraction, take a premium,
   take off, taper off, tare, time discount, trade discount, tret,
   underselling, write off, write-off



Bouvier's Law Dictionary, Revised 6th Ed (1856):

REBATE, mer. law. Discount; the abatement of interest in consequence of
prompt payment. Merch. Dict. h.t.