Source : Webster's Revised Unabridged Dictionary (1913)

Proin \Proin\ (proin), v. t. [See {Prune} to trim.]
   To lop; to trim; to prune; to adorn. [Obs.] --Chaucer.

         The sprigs that did about it grow He proined from the
         leafy arms.                              --Chapman.

Proin \Proin\, v. i.
   To employed in pruning. [Obs.]