The Collaborative International Dictionary of English v.0.48:

Expedience \Ex*pe"di*ence\, Expediency \Ex*pe"di*en*cy\,, n.
   1. The quality of being expedient or advantageous; fitness or
      suitableness to effect a purpose intended; adaptedness to
      self-interest; desirableness; advantage; advisability; --
      sometimes contradistinguished from moral rectitude or
      principle.
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            Divine wisdom discovers no expediency in vice.
                                                  --Cogan.
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            To determine concerning the expedience of action.
                                                  --Sharp.
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            Much declamation may be heard in the present day
            against expediency, as if it were not the proper
            object of a deliberative assembly, and as if it were
            only pursued by the unprincipled.     --Whately.
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   2. Expedition; haste; dispatch. [Obs.]
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            Making hither with all due expedience. --Shak.
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   3. An expedition; enterprise; adventure. [Obs.]
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            Forwarding this dear expedience.      --Shak.
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WordNet (r) 3.0 (2006):

expediency
    n 1: the quality of being suited to the end in view [syn:
         expedience, expediency] [ant: inexpedience,
         inexpediency]

Moby Thesaurus II by Grady Ward, 1.0:

27 Moby Thesaurus words for "expediency":
   appositeness, appropriateness, aptness, careworn, convenience,
   dernier ressort, design, expedient, fitness, makeshift, measure,
   meetness, order, propitiousness, propriety, recourse, resort,
   rightness, shift, step, stopgap, strategy, substitute, suitability,
   suitableness, surrogate, tactic