The Collaborative International Dictionary of English v.0.48:

Plenarty \Plen"ar*ty\, n.
   The state of a benefice when occupied. --Blackstone.
   [1913 Webster]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

PLENARTY, eccl. law. Signifies that a benefice is full. Vide Avoidance.