The Collaborative International Dictionary of English v.0.48:

Transaction \Trans*ac"tion\, n. [L. transactio, fr. transigere,
   transactum, to drive through, carry through, accomplish,
   transact; trans across, over + agere to drive; cf. F.
   transaction. See Act, Agent.]
   1. The doing or performing of any business; management of any
      affair; performance.
      [1913 Webster]

   2. That which is done; an affair; as, the transactions on the
      exchange.
      [1913 Webster]

   3. (Civil Law) An adjustment of a dispute between parties by
      mutual agreement.
      [1913 Webster]

   Transaction of a society, the published record of what it
      has done or accomplished.
      [1913 Webster]

   Syn: Proceeding; action; process.

   Usage: Transaction, Proceeding. A transaction is
          something already done and completed; a proceeding is
          either something which is now going on, or, if ended,
          is still contemplated with reference to its progress
          or successive stages.
          [1913 Webster]

   Note: " We the word proceeding in application to an affray in
         the street, and the word transaction to some commercial
         negotiation that has been carried on between certain
         persons. The proceeding marks the manner of proceeding,
         as when we speak of the proceedings in a court of law.
         The transaction marks the business transacted; as, the
         transactions on the Exchange." --Crabb.
         [1913 Webster]

WordNet (r) 3.0 (2006):

transaction
    n 1: the act of transacting within or between groups (as
         carrying on commercial activities); "no transactions are
         possible without him"; "he has always been honest is his
         dealings with me" [syn: transaction, dealing,
         dealings]

Moby Thesaurus II by Grady Ward, 1.0:

110 Moby Thesaurus words for "transaction":
   accomplished fact, accomplishment, accord, achievement, act, acta,
   action, administration, adventure, affair, agreement, annals,
   arrangement, bargain, binding agreement, blow, bond, business,
   business deal, carrying out, cartel, collective agreement,
   commercial transaction, commission, compact, completion, concern,
   concernment, conduct, consortium, contract, convention, coup,
   covenant, covenant of salt, deal, dealing, dealings, deed, dicker,
   discharge, dispatch, doing, doings, effectuation, effort,
   employment contract, enactment, endeavor, enforcement, enterprise,
   execution, exploit, fait accompli, feat, formal agreement,
   fulfillment, gest, go, goings-on, hand, handiwork, handling,
   implementation, interest, ironclad agreement, job, legal agreement,
   legal contract, management, maneuver, matter, measure, minutes,
   move, mutual agreement, negotiation, observance, operation,
   overt act, package deal, pact, paction, passage, performance,
   perpetration, proceeding, proceedings, production, promise,
   prosecution, protocol, records, res gestae, step, stipulation,
   stroke, stunt, thing, thing done, tour de force, transactions,
   turn, understanding, undertaking, union contract, valid contract,
   wage contract, work, works



The Free On-line Dictionary of Computing (30 December 2018):

transaction

   A unit of interaction with a DBMS or similar system.  It
   must be treated in a coherent and reliable way independent of
   other transactions.  See atomic.


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

TRANSACTION, contracts, civil law. An agreement between two or more persons,
who for the purpose of preventing or putting an end to a law suit, adjust
their differences by mutual consent, in the manner which they agree on; in
Louisiana this contract must be reduced to writing. Civil Code of Louis,
3038.
     2. Transactions regulate only the differences which appear to be
clearly comprehended in them by the intentions of the parties, whether they
be explained in a general or particular manner, unless it be the necessary
consequence of what is expressed; and they do not extend to differences
which the parties, never intended to include in them. Id. 3040.
     3. To transact, a man must have the capacity to dispose of the things
included in the transaction. Id. 3039; 1 Domat, Lois Civiles, liv. 1, t. 13,
s. 1; Dig. lib. 2, t. 15, l. 1; Code lib. 2, t. 4, 1. 41. In the common law
this is called a compromise. (q.v.)