The Collaborative International Dictionary of English v.0.48:

Allegation \Al`le*ga"tion\, n. [L. allegatio, fr. allegare,
   allegatum, to send a message, cite; later, to free by giving
   reasons; ad + legare to send, commission. Cf. Allege and
   Adlegation.]
   1. The act of alleging or positively asserting.
      [1913 Webster]

   2. That which is alleged, asserted, or declared; positive
      assertion; formal averment
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            I thought their allegation but reasonable. --Steele.
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   3. (Law) A statement by a party of what he undertakes to
      prove, -- usually applied to each separate averment; the
      charge or matter undertaken to be proved.
      [1913 Webster]

WordNet (r) 3.0 (2006):

allegation
    n 1: (law) a formal accusation against somebody (often in a
         court of law); "an allegation of malpractice"
    2: statements affirming or denying certain matters of fact that
       you are prepared to prove [syn: allegation, allegement]