Possible Definitions:
1. Plain (v. i.) To lament; to bewail; to complain.
2. Plain (v. t.) To lament; to mourn over; as, to plain a loss.
3. Plain (superl.) Without elevations or depressions; flat; level; smooth; even. See Plane.
4. Plain (superl.) Open; clear; unencumbered; equal; fair.
5. Plain (superl.) Not intricate or difficult; evident; manifest; obvious; clear; unmistakable.
6. Plain (superl.) Void of extraneous beauty or ornament; without conspicious embellishment; not rich; simple.
7. Plain (superl.) Not highly cultivated; unsophisticated; free from show or pretension; simple; natural; homely; common.
8. Plain (superl.) Free from affectation or disguise; candid; sincere; artless; honest; frank.
9. Plain (superl.) Not luxurious; not highly seasoned; simple; as, plain food.
10. Plain (superl.) Without beauty; not handsome; homely; as, a plain woman.
11. Plain (superl.) Not variegated, dyed, or figured; as, plain muslin.
12. Plain (superl.) Not much varied by modulations; as, a plain tune.
13. Plain (adv.) In a plain manner; plainly.
14. Plain (a.) Level land; usually, an open field or a broad stretch of land with an even surface, or a surface little varied by inequalities; as, the plain of Jordan; the American plains, or prairies.
15. Plain (a.) A field of battle.
16. Plain (v.) To plane or level; to make plain or even on the surface.
17. Plain (v.) To make plain or manifest; to explain.