plain

American Heritage® Dictionary of the English Language, Fourth Edition

1. adj. Free from obstructions; open; clear: in plain view.
2. adj. Obvious to the mind; evident: make one's intention plain. See Synonyms at apparent.
3. adj. Not elaborate or complicated; simple: plain food.
4. adj. Straightforward; frank or candid: plain talk.
5. adj. Not mixed with other substances; pure: plain water.
6. adj. Common in rank or station; average; ordinary: a plain man.
7. adj. Not pretentious; unaffected.
8. adj. Marked by little or no ornamentation or decoration.
9. adj. Not dyed, twilled, or patterned: a plain fabric.
10. adj. Lacking beauty or distinction: a plain face.
11. adj. Sheer; utter; unqualified: plain stupidity.
12. adj. Archaic Having no visible elevation or depression; flat; level.
13. n. An extensive, level, usually treeless area of land.
14. n. A broad level expanse, as a part of the sea floor or a lunar mare.
15. n. Something free of ornamentation or extraneous matter.
16. adv. Informal Clearly; simply: plain stubborn.

Century Dictionary and Cyclopedia

1. Flat; level: smooth; even; free from elevations and depressions: as, a plain surface or country.
2. Open; unobstructed by intervening barriers or defenses.
3. Easy; free from intricacies or difficulties: as, plain exercises in shorthand.
4. Undisguised; frank; sincere; unreserved.
5. Clear; evident; manifest; easily perceived or understood: as, to make one's meaning plain; it was plain he was offended.
6. Unqualified: undisguised; unmistakable; sheer; downright; absolute.
7. Without a figured pattern; unornamented with decorative patterns or designs; also, when applied to fabrics, untwilled or uncolored: as. plain black cloth; plain muslin.
8. Void of ornament or bright color; without embellishment; simple; unadorned.
9. Without beauty; homely: as, she is plain, but clever.
10. Artless; simple; unlearned; without artifice or affectation; unsophisticated.
11. Not highly seasoned; not rich; not luxuriously dressed: as, a plain diet.
12. Incomplex; simple.
13. In card-playing, not trumps; lay: as, a plain card; a plain suit.
14. Whole-colored; not variegated: as, plain white eggs.
15. Smooth; unstriate, as muscular fiber.
16. Embroidery in the same color as the ground.
17. Clear, Evident, etc. (see manifest), distinct, patent, unmistakable, unequivocal, unambiguous, explicit, intelligible.
18. Unvarnished, unem-bellished.
19. n. An extent of level, or nearly level, land; a region not noticeably diversified with mountains, hills, or valleys. The Plains, in North America, are the lands lying between the 104th meridian and the eastern base of the Rocky Mountains. This region has a gradual slope from the mountains to the Missouri and Mississippi rivers, but is nowhere broken by any conspicuous ranges of hills. It is a region of small precipitation, wooded only along the banks of the streams, and not always there. The Plains and the prairies are not properly the same, from either a geographical or a climato-logical point of view. See prairie.
20. n. A field; especially, a field of battle.
21. n. An open space surrounded by houses: as, St. Mary's Plain; the Theater Plain, in Norwich.
22. In a plain manner; plainly; clearly; openly; frankly; bluntly.
23. To make plain, level, or even; smooth; clear.
24. To make plain or clear; explain.
25. To lament; wail; mourn.
26. To whinny: said of a horse.
27. To lament; bewail; bemoan; mourn over.
28. In old music, said of certain graces or embellishments, like the beat, backfall, etc., when without extension by a shake: opposed to shaked. Also called smooth.

Wiktionary

1. adv. colloquial Simply
2. v. poetic To lament, bewail.
3. n. An expanse of land with relatively low relief.
4. n. obsolete A plane.
5. v. obsolete, transitive To plane or level; to make plain or even on the surface.
6. v. obsolete, transitive To make plain or manifest; to explain.

GNU Webster's 1913

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

WordNet 3.0

1. adj. not mixed with extraneous elements
2. n. extensive tract of level open land
3. adj. not elaborate or elaborated; simple.
4. adj. lacking embellishment or ornamentation
5. adj. free from any effort to soften to disguise
6. adj. clearly revealed to the mind or the senses or judgment
7. v. express complaints, discontent, displeasure, or unhappiness
8. adv. unmistakably (`plain' is often used informally for `plainly')
9. adj. lacking in physical beauty or proportion
10. adj. lacking patterns especially in color
11. n. a basic knitting stitch