The Collaborative International Dictionary of English v.0.48:

Plenary \Ple"na*ry\, a. [LL. plenarius, fr. L. plenus full. See
   Plenty.]
   Full; entire; complete; absolute; as, a plenary license;
   plenary authority.
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         A treatise on a subject should be plenary or full. --I.
                                                  Watts.
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   Plenary indulgence (R. C. Ch.), an entire remission of
      temporal punishment due to, or canonical penance for, all
      sins.

   Plenary inspiration. (Theol.) See under Inspiration.
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