The Collaborative International Dictionary of English v.0.48:

Constituent \Con*stit"u*ent\ (k[o^]n*st[i^]t"[-u]*[-e]nt), a.
   [L. constituens, -entis, p. pr. See Constitute.]
   1. Serving to form, compose, or make up; elemental;
      component.
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            Body, soul, and reason are the three parts
            necessarily constituent of a man.     --Dryden.
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   2. Having the power of electing or appointing.
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            A question of right arises between the constituent
            and representative body.              --Junius.
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The Collaborative International Dictionary of English v.0.48:

Constituent \Con*stit"u*ent\, n.
   1. The person or thing which constitutes, determines, or
      constructs.
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            Their first composure and origination require a
            higher and nobler constituent than chance. --Sir M.
                                                  Hale
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   2. That which constitutes or composes, as a part, or an
      essential part; a component; an element.
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            We know how to bring these constituents together,
            and to cause them to form water.      --Tyndall.
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   3. One for whom another acts; especially, one who is
      represented by another in a legislative assembly; --
      correlative to representative.
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            The electors in the district of a representative in
            Congress, or in the legislature of a State, are
            termed his constituents.              --Abbot.
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            To appeal from the representatives to the
            constituents.                         --Macaulay.
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   4. (Law) A person who appoints another to act for him as
      attorney in fact. --Burrill.
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WordNet (r) 3.0 (2006):

constituent
    adj 1: constitutional in the structure of something (especially
           your physical makeup) [syn: constituent(a),
           constitutional, constitutive(a), organic]
    n 1: an artifact that is one of the individual parts of which a
         composite entity is made up; especially a part that can be
         separated from or attached to a system; "spare components
         for cars"; "a component or constituent element of a system"
         [syn: component, constituent, element]
    2: a member of a constituency; a citizen who is represented in a
       government by officials for whom he or she votes; "needs
       continued support by constituents to be re-elected"
    3: something determined in relation to something that includes
       it; "he wanted to feel a part of something bigger than
       himself"; "I read a portion of the manuscript"; "the smaller
       component is hard to reach"; "the animal constituent of
       plankton" [syn: part, portion, component part,
       component, constituent]
    4: (grammar) a word or phrase or clause forming part of a larger
       grammatical construction [syn: constituent, grammatical
       constituent]
    5: an abstract part of something; "jealousy was a component of
       his character"; "two constituents of a musical composition
       are melody and harmony"; "the grammatical elements of a
       sentence"; "a key factor in her success"; "humor: an
       effective ingredient of a speech" [syn: component,
       constituent, element, factor, ingredient]

Moby Thesaurus II by Grady Ward, 1.0:

97 Moby Thesaurus words for "constituent":
   ab ovo, adjunct, adoptive, air, appointive, appurtenance, aspect,
   atom, atomic particles, basal, basic, brute matter, building block,
   census, chemical element, choosing, choosy, circumstance,
   component, composition, constituents, constitutive, content,
   contents, detail, discriminating, division, divisions, earth,
   eclectic, elective, electoral, element, elemental, elementary,
   elementary particle, elementary unit, elements, essential, factor,
   feature, fire, fixings, formative, fraction, fundamental,
   fundamental particle, gut, guts, hyle, hypostasis, index,
   ingredient, ingredients, innards, insides, integral, integrant,
   inventory, item, items, list, makings, material, material world,
   materiality, matter, molecule, monad, natural world, nature,
   of the essence, original, part, part and parcel, particular, parts,
   physical world, plenum, portion, primal, primary, primitive,
   radical, selecting, selective, specialty, stuff, substance,
   substantial, substantive, substratum, the four elements,
   underlying, unit of being, water, whole



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

CONSTITUENT. He who gives authority to another to act for him. 1 Bouv. Inst.
n. 893.
     2. The constituent is bound with whatever his attorney does by virtue
of his authority. The electors of a member of the legislature are his
constituents, to whom he is responsible for his legislative acts.