PLAIN (6)

Plain, v. t. [imp. & p. p. Plained (�); p. pr. & vb. n. Plaining.] [[Cf. Plane, v.]] 1. 1. To plane or level; to make plain or even on the surface.
We would rake Europe rather, plain the East. Wither. 2. 2. To make plain or manifest; to explain.
What's dumb in show, I'll plain in speech. Shak.