(plān) adjective
1. Having no noticeable elevation or depression; flat; smooth.
2. Presenting few difficulties; easy.
3. Clear; understandable: plain English; also, straightforward; guileless.
4. Lowly in condition or station; unlearned.
5. Having no conspicuous ornamentation; unadorned; unvariegated; in the case of cloths, not figured or twilled.
6. Homely.
7. Not rich, as food.
—noun An expanse of level, treeless land; a prairie. ♦ Homophone: plane. [<OF <L planus flat; noun, doublet of PLAN]
—plain′ly adverb
—plain′·ness noun Synonyms (adj.): clear, distinct, explicit, intelligible, perspicuous, straightforward, transparent, unadorned, unambiguous, unequivocal. That is clear which offers no impediment to vision
—is not dim, dark, or obscure. Transparent refers to the medium through which a substance is seen, clear to the substance itself, without reference to anything to be seen through it; we speak of a stream as clear when we think of the water itself; we speak of it as transparent with reference to the ease with which we see objects at the bottom. Plain is level to the thought, so that one goes straight on without difficulty or hindrance; as, plain language; a plain statement; a clear explanation. Perspicuous is often equivalent to plain, but plain never wholly loses the meaning of unadorned, so that we can say the style is perspicuous even if highly ornate, when we could not call it at once ornate and plain. See APPARENT, BLANK, CLEAR, EVIDENT, EXPLICIT, HORIZONTAL, LEVEL, MANIFEST, NOTORIOUS, RUSTIC, SMOOTH. Antonyms: see synonyms for EQUIVOCAL, OBSCURE.

(plān) v.i.
1. Dial. To complain.
2. Obs. To mourn. ♦ Homophone: plane. [<OF plaign-, stem of plaindre <L plangere beat the breast, lament]