The Collaborative International Dictionary of English v.0.48:

Plausibility \Plau`si*bil"i*ty\, n. [Cf. F. plausibilit['e].]
   1. Something worthy of praise. [Obs.]
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            Integrity, fidelity, and other gracious
            plausibilities.                       --E. Vaughan.
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   2. The quality of being plausible; speciousness.
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            To give any plausibility to a scheme. --De Quincey.
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   3. Anything plausible or specious. --R. Browning.
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WordNet (r) 3.0 (2006):

plausibility
    n 1: apparent validity [syn: plausibility, plausibleness]
         [ant: implausibility, implausibleness]