Plain \Plain\, v. t. [imp. & p. p. {Plained}; p. pr. & vb. n. {Plaining}.] [Cf. {Plane}, v.] 1. To plane or level; to make plain or even on the surface. [R.] We would rake Europe rather, plain the East. --Wither. 2. To make plain or manifest; to explain. What's dumb in show, I'll plain in speech. --Shak. Plaining \Plain"ing\, n. Complaint. [Poetic] --Shak. Plaining \Plain"ing\, a. Complaining. [Poetic] --Bryant.