The Collaborative International Dictionary of English v.0.48:

Agreement \A*gree"ment\, n. [Cf. F. agr['e]ment.]
   1. State of agreeing; harmony of opinion, statement, action,
      or character; concurrence; concord; conformity; as, a good
      agreement subsists among the members of the council.
      [1913 Webster]

            What agreement hath the temple of God with idols ?
                                                  --2 Cor. vi.
                                                  16.
      [1913 Webster]

            Expansion and duration have this further agreement.
                                                  --Locke.
      [1913 Webster]

   2. (Gram.) Concord or correspondence of one word with another
      in gender, number, case, or person.
      [1913 Webster]

   3. (Law)
      (a) A concurrence in an engagement that something shall be
          done or omitted; an exchange of promises; mutual
          understanding, arrangement, or stipulation; a
          contract.
      (b) The language, oral or written, embodying reciprocal
          promises. --Abbott. Brande & C.
          [1913 Webster]

   Syn: Bargain; contract; compact; stipulation.
        [1913 Webster]

WordNet (r) 3.0 (2006):

agreement
    n 1: the statement (oral or written) of an exchange of promises;
         "they had an agreement that they would not interfere in
         each other's business"; "there was an understanding between
         management and the workers" [syn: agreement,
         understanding]
    2: compatibility of observations; "there was no agreement
       between theory and measurement"; "the results of two tests
       were in correspondence" [syn: agreement, correspondence]
    3: harmony of people's opinions or actions or characters; "the
       two parties were in agreement" [syn: agreement, accord]
       [ant: disagreement, dissension, dissonance]
    4: the thing arranged or agreed to; "they made arrangements to
       meet in Chicago" [syn: agreement, arrangement]
    5: the determination of grammatical inflection on the basis of
       word relations [syn: agreement, concord]
    6: the verbal act of agreeing [ant: disagreement]

Moby Thesaurus II by Grady Ward, 1.0:

299 Moby Thesaurus words for "agreement":
   Anschluss, OK, acceptance, accession, acclamation, accommodation,
   accompaniment, accord, accordance, acquiescence, adaptation,
   adaption, addition, adjustment, affiliation, affinity, affirmation,
   affirmative, affirmative voice, agape, agglomeration, aggregation,
   agreement, agreement in principle, agreement of all, alikeness,
   alliance, amalgamation, amity, analogy, aping, approach,
   approbation, approval, approximation, arrangement, assent,
   assentation, assimilation, association, aye, bargain,
   binding agreement, blend, blending, blessing, bond,
   bonds of harmony, brotherly love, cabal, cahoots, caritas, cartel,
   cement of friendship, centralization, charity, chime, chorus,
   closeness, co-working, coaction, coalescence, coalition,
   coequality, coetaneity, coetaneousness, coevalneity, coevalness,
   coexistence, coincidence, collaboration, collective agreement,
   collectivity, collusion, combination, combine, combined effort,
   combo, commitment, common assent, common consent, communion,
   community, community of interests, compact, comparability,
   comparison, compatibility, compliance, composition, concert,
   concerted action, concomitance, concord, concordance, concordat,
   concourse, concurrence, confederacy, confederation, confluence,
   conformance, conformation other-direction, conformity,
   congeniality, congeries, conglomeration, congruence, congruity,
   conjugation, conjunction, connivance, consensus, consensus gentium,
   consensus of opinion, consensus omnium, consent, consentaneity,
   consilience, consistency, consolidation, consonance, consortium,
   conspiracy, contemporaneity, contemporaneousness, contract,
   convention, conventionality, cooperation, copying, correspondence,
   covenant, covenant of salt, deal, dicker, eagerness, ecumenism,
   embodiment, empathy, employment contract, encompassment,
   endorsement, engagement, enosis, entente, equality, equivalence,
   esprit, esprit de corps, federalization, federation,
   feeling of identity, fellow feeling, fellowship, flexibility,
   formal agreement, frictionlessness, fusion, general acclamation,
   general agreement, general consent, general voice, good vibes,
   good vibrations, happy family, harmony, hearty assent, homogeneity,
   homoousia, hookup, identity, imitation, inclusion, incorporation,
   indistinguishability, integration, ironclad agreement, junta,
   keeping, kinship, league, legal agreement, legal contract,
   like-mindedness, likeness, likening, line, love, malleability,
   marriage, meeting of minds, meld, melding, merger, metaphor,
   mimicking, mutual agreement, mutual understanding, mutuality,
   nearness, no difference, obedience, obligation, observance, okay,
   one accord, one voice, oneness, orthodoxy, package, package deal,
   pact, paction, parallelism, parasitism, parity, peace, permission,
   pliancy, preengagement, promise, promptitude, promptness, protocol,
   rapport, rapprochement, ratification, readiness, reciprocity,
   recognizance, reconcilement, reconciliation, resemblance,
   same mind, sameness, sanction, saprophytism, self-identity,
   selfhood, selfness, selfsameness, semblance, settlement, sharing,
   similarity, simile, similitude, simulation, simultaneity,
   single voice, solidarity, solidification, stipulation, strictness,
   submission, support, symbiosis, sympathy, symphony, synchronism,
   synchronization, syncretism, syndication, syneresis, synergy,
   synonymity, synonymousness, synonymy, synthesis, team spirit,
   tie-up, total agreement, traditionalism, transaction, treaty, tune,
   unanimity, unanimousness, understanding, undertaking,
   ungrudgingness, unification, uniformity, union, union contract,
   unison, united action, unity, universal agreement, unloathness,
   unreluctance, valid contract, verbal agreement, wage contract,
   warm assent, wedding, welcome, willingness



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

AGREEMENT, contract. The consent of two or more persons concurring,
respecting the transmission of some property, right or benefit, with a view
of contracting an obligation. Bac. Ab. h.t.; Com. Dig. h.t.; Vin. Ab. h.t.;
Plowd. 17; 1 Com. Contr. 2; 5 East's R. 16. It will be proper to consider,
1, the requisites of an agreement; 2, the kinds of agreements; 3, how they
are annulled.
     2.-1. To render an agreement complete six things must concur; there
must be, 1, a person able to contract; 2, a person able to be contracted
with; 3, a thing to be contracted for; 4, a lawful consideration, or quid
pro quo; 5, words to express the agreement; 6, the assent of the contracting
parties. Plowd. 161; Co. Litt. 35, b.
     3.-2. As to their form, agreements are of two kinds; 1, by parol, or,
in writing, as contradistinguished from specialties; 2, by specialty, or
under seal. In relation to their performance, agreements are executed or
executory. An agreement is said to be executed when two or more persons make
over their respective rights in a thing to one another, and thereby change
the property therein, either presently and at once, or at a future time,
upon some event that shall give it full effect, without either party
trusting to the other; as where things are bought, paid for and delivered.
Executory agreements, in the ordinary acceptation of the term, are such
contracts as rest on articles, memorandums, parol promises, or undertakings,
and the like, to be performed  in future, or which are entered into
preparatory to more solemn and formal alienations of property. Powell on
Cont. Agreements are also conditional and unconditional. They are
conditional when some condition must be fulfilled before they can have full
effect; they are unconditional when there is no condition attached;
     4.-3. Agreements are annulled or rendered of no effect, first, by the
acts of the parties, as, by payment; release - accord and satisfaction;
rescission, which is express or implied; 1 Watts & Serg. 442; defeasance; by
novation: secondly, by the acts of the law, as, confusion; merger; lapse of
time; death, as when a man who has bound himself to teach an apprentice,
dies; extinction of the thing which is the subject of the contract, as, when
the agreement is to deliver a certain horse and before the time of delivery
he dies. See Discharge of a Contract.
     5. The writing or instrument containing an agreement is also called an
agreement, and sometimes articles of agreement.(q.v.)
     6. It is proper, to remark that there is much difference between an
agreement and articles of agreement which are only evidence of it. From the
moment that the parties have given their consent, the agreement or contract
is formed, and, whether it can be proved or not, it has not less the quality
to bind both contracting parties. A want of proof does not make it null,
because that proof may be supplied aliunde, and the moment it is obtained,
the contract may be enforced.
     7. Again, the agreement may be mull, as when it was obtained by fraud,
duress, and the like; and the articles of agreement may be good, as far as
the form is concerned. Vide Contract. Deed; Guaranty; Parties to Contracts.