The Collaborative International Dictionary of English v.0.48:
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.
(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."
(c) Free from affectation or disguise; candid; sincere;
artless; honest; frank. "An honest mind, and plain."
(d) Not luxurious; not highly seasoned; simple; as, plain
(e) Without beauty; not handsome; homely; as, a plain
(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.]
Plain chant (Mus.) Same as Plain song, below.
Plain chart (Naut.), a chart laid down on Mercator's
(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 sewing, sewing of seams by simple and common
stitches, in distinct from fancy work, embroidery, etc.;
-- distinguished also from designing and fitting garments.
(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.