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.
   [1913 Webster]

         A treatise on a subject should be plenary or full. --I.
                                                  Watts.
   [1913 Webster]

   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.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Plenary \Ple"na*ry\, n. (Law)
   Decisive procedure. [Obs.]
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

69 Moby Thesaurus words for "plenary":
   SRO, absolute, brimful, brimming, bulging, bursting, capacity,
   chock-full, chuck-full, comprehensive, congested, consequential,
   considerable, cram-full, crammed, deep, exhaustive, farci, filled,
   flush, full, full to bursting, grand, grave, great, heavy,
   illimitable, intense, irresistible, jam-packed, limitless, main,
   maximum, mighty, no strings, open, overfull, overstuffed, packed,
   packed like sardines, perfect, powerful, ready to burst, replete,
   round, satiated, saturated, serious, soaked, standing room only,
   strong, stuffed, surfeited, swollen, topful, total, unbound,
   unbounded, uncircumscribed, unconditional, unconditioned,
   unconfined, unequivocal, unlimited, unmeasured, unqualified,
   unrestricted, wide-open, without strings