The Collaborative International Dictionary of English v.0.48:

efficience \ef*fi"cience\ ([e^]f*f[i^]sh"ens), efficiency
\ef*fi"cien*cy\ ([e^]f*f[i^]sh"en*s[y^]), n. [L. efficientia.]
   1. The quality of being efficient or producing an effect or
      effects; efficient power; effectual agency.
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            The manner of this divine efficiency being far above
            us.                                   --Hooker.
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   2. (Mech.) The ratio of useful work to energy expended.
      --Rankine.
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   efficiency of a heat engine, the ratio of the work done by
      an engine, to the work due to the heat supplied to it.
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