The Collaborative International Dictionary of English v.0.48:

Plein \Plein\, a.
   Plan. [Obs.] --Chaucer.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Plein \Plein\, v. i. & t.
   To complain. See Plain. [Obs.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Plein \Plein\, a. [OF. & F., fr. L. plenus.]
   Full; complete. [Obs.] "Plein remission." --Chaucer. --
   Plein"ly, adv.
   [1913 Webster]