The Collaborative International Dictionary of English v.0.48:

installment \in*stall"ment\, instalment \in*stal"ment\, n.
   1. The act of installing; installation.
      [1913 Webster]

            Take oaths from all kings and magistrates at their
            installment, to do impartial justice by law.
                                                  --Milton.
      [1913 Webster]

   2. The seat in which one is placed. [Obs.]
      [1913 Webster]

            The several chairs of order, look, you scour; . . .
            Each fair installment, coat, and several crest
            With loyal blazon, evermore be blest. --Shak.
      [1913 Webster]

   3. A portion of a debt, or sum of money, which is divided
      into portions that are made payable at different times;
      that portion of a debt payed back in any one payment; as,
      the next installment is due January first. Payment by
      installment is payment by parts at different times, the
      amounts and times being often definitely stipulated.
      --Bouvier.
      [1913 Webster +PJC]

   4. a part of a broadcast serial. [WordNet sense 1]

   Syn: episode.
        [WordNet 1.5]

   5. a part of a published serial. [WordNet sense 2]
      [WordNet 1.5]

WordNet (r) 3.0 (2006):

installment
    n 1: a payment of part of a debt; usually paid at regular
         intervals
    2: a part of a broadcast serial [syn: episode, installment,
       instalment]
    3: a part of a published serial [syn: installment,
       instalment]
    4: the act of installing something (as equipment); "the
       telephone installation took only a few minutes" [syn:
       installation, installing, installment, instalment]

Moby Thesaurus II by Grady Ward, 1.0:

124 Moby Thesaurus words for "installment":
   accedence, accession, acquitment, acquittal, acquittance, adjunct,
   amortization, amortizement, anchorage, article, binder, book, cash,
   cash payment, chapter, clause, clearance, colonization, column,
   coming out, component, contingent, coronation, cross section,
   curtain raiser, debt service, debut, defrayal, defrayment, deposit,
   detachment, detail, disbursal, discharge, division, dole,
   doling out, down payment, earnest, earnest money, embarkation,
   embarkment, enthronement, establishment, fascicle,
   first appearance, fixation, floating, flotation, foundation,
   fraction, hire purchase, hire purchase plan, inaugural address,
   inauguration, induction, initiation, installation,
   installment plan, instatement, interest payment, introduction,
   investiture, item, launching, liquidation, livraison, lodgment,
   maiden speech, monthly payments, mooring, never-never, opener,
   paragraph, parcel, part, particular, passage, paying, paying off,
   paying out, paying up, payment, payment in kind, payoff, peopling,
   percentage, phrase, placement, plantation, population, portion,
   preliminary, prepayment, quadrant, quarter, quarterly payments,
   quittance, quota, random sample, regular payments, remainder,
   remittance, retirement, sample, sampling, satisfaction, section,
   sector, segment, serial, settlement, settling, share,
   sinking-fund payment, spot cash, subdivision, subgroup, subspecies,
   taking office, unveiling, verse, volume, weekly payments