The Collaborative International Dictionary of English v.0.48:

Moiety \Moi"e*ty\ (moi"[-e]*t[y^]), n.; pl. Moieties
   (moi"[-e]*t[i^]z). [F. moiti['e], L. medietas, fr. medius
   middle, half. See Mid, a., and cf. Mediate, Mediety.]
   1. One of two equal parts; a half; as, a moiety of an estate,
      of goods, or of profits; the moiety of a jury, or of a
      nation. --Shak.
      [1913 Webster]

            The more beautiful moiety of his majesty's subject.
                                                  --Addison.
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   2. An indefinite part; a small part. --Shak.
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The Collaborative International Dictionary of English v.0.48:

Residue \Res"i*due\ (r?z"?-d?), n. [F. r['e]sidu, L. residuum,
   fr. residuus that is left behind, remaining, fr. residere to
   remain behind. See Reside, and cf. Residuum.]
   1. That which remains after a part is taken, separated,
      removed, or designated; remnant; remainder.
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            The residue of them will I deliver to the sword.
                                                  --Jer. xv. 9.
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            If church power had then prevailed over its victims,
            not a residue of English liberty would have been
            saved.                                --I. Taylor.
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   2. (Law) That part of a testeator's estate wwhich is not
      disposed of in his will by particular and special legacies
      and devises, and which remains after payment of debts and
      legacies.
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   3. (Chem.) That which remains of a molecule after the removal
      of a portion of its constituents; hence, an atom or group
      regarded as a portion of a molecule; a moiety or
      group; -- used as nearly equivalent to radical, but in
      a more general sense.
      [1913 Webster +PJC]

   Note: The term radical is sometimes restricted to groups
         containing carbon, the term residue and moiety being
         applied to the others.
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   4. (Theory of Numbers) Any positive or negative number that
      differs from a given number by a multiple of a given
      modulus; thus, if 7 is the modulus, and 9 the given
      number, the numbers -5, 2, 16, 23, etc., are residues.
      [1913 Webster]

   Syn: Rest; remainder; remnant; balance; residuum; remains;
        leavings; relics.
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WordNet (r) 3.0 (2006):

moiety
    n 1: one of two (approximately) equal parts [syn: moiety,
         mediety]
    2: one of two basic subdivisions of a tribe