Source : Webster's Revised Unabridged Dictionary (1913)

Plain \Plain\, a. [Compar. {Plainer}; superl. {Plainest}.] [F.,
   level, flat, fr. L. planus, perhaps akin to E. floor. Cf.
   {Llano}, {Piano}, {Plan}, {Plane} level, a level surface.]
   1. Without elevations or depressions; flat; level; smooth;
      even. See {Plane}.

            The crooked shall be made straight, and the rough
            places plain.                         --Isa. xl. 4.

   2. Open; clear; unencumbered; equal; fair.

            Our troops beat an army in plain fight. --Felton.

   3. Not intricate or difficult; evident; manifest; obvious;
      clear; unmistakable. ``'T is a plain case.'' --Shak.

   4.
      (a) Void of extraneous beauty or ornament; without
          conspicious embellishment; not rich; simple.
      (b) Not highly cultivated; unsophisticated; free from show
          or pretension; simple; natural; homely; common.
          ``Plain yet pious Christians.'' --Hammond. ``The plain
          people.'' --A. Lincoln.
      (c) Free from affectation or disguise; candid; sincere;
          artless; honest; frank. ``An honest mind, and plain.''
          --Shak.
      (d) Not luxurious; not highly seasoned; simple; as, plain
          food.
      (e) Without beauty; not handsome; homely; as, a plain
          woman.
      (f) Not variegated, dyed, or figured; as, plain muslin.
      (g) Not much varied by modulations; as, a plain tune.

   {Plain battle}, open battle; pitched battle. [Obs.]
      --Chaucer.

   {Plain chant} (Mus.) Same as {Plain song}, below.

   {Plain chart} (Naut.), a chart laid down on Mercator's
      projection.

   {Plain dealer}.
      (a) One who practices plain dealing.
      (b) A simpleton. [Obs.] --Shak.

   {Plain dealing}. See under {Dealing}.

   {Plain molding} (Join.), molding of which the surfaces are
      plain figures.

   {Plain sewing}, sewing of seams by simple and common
      stitches, in distinct from fancy work, embroidery, etc.;
      -- distinguished also from designing and fitting garments.
      

   {Plain song}.
      (a) The Gregorian chant, or {canto fermo}; the prescribed
          melody of the Roman Catholic service, sung in unison,
          in tones of equal length, and rarely extending beyond
          the compass of an octave.
      (b) A simple melody.

   {Plain speaking}, plainness or bluntness of speech.

   Syn: Level; flat; smooth; open; artless; unaffected;
        undisguised; frank; sincere; honest; candid; ingenuous;
        unembellished; downright; blunt; clear; simple;
        distinct; manifest; obvious; apparent. See {Manifest}.