13. (adv.)plain clearly and simply: They're just plain stupid.
14. (n.)plain an area of land not significantly higher than adjacent areas and with relatively minor differences in elevation, commonly less than 500 ft. (150 m), within the area.
15. plain The Plains,
Etymology: (1720–30; cf. F)
Definition of 'Plain'
Princeton's WordNet
1. (noun)plain, field, champaign extensive tract of levelopenland "they emerged from the woods onto a vast open plain"; "he longed for the fields of his youth"
3. (adj)apparent, evident, manifest, patent, plain, unmistakable clearly revealed to the mind or the senses or judgment "the effects of the drought are apparent to anyone who sees the parched fields"; "evident hostility"; "manifest disapproval"; "patent advantages"; "made his meaning plain"; "it is plain that he is no reactionary"; "in plain view"
4. (adj)plain not elaborate or elaborated; simple "plain food"; "stuck to the plain facts"; "a plain blue suit"; "a plain rectangular brick building"
5. (adj)plain, unpatterned lacking patterns especially in color
6. (adj)plain, sheer, unmingled, unmixed not mixed with extraneous elements "plain water"; "sheer wine"; "not an unmixed blessing"
7. (adj)plain, unvarnished free from any effort to soften to disguise "the plain and unvarnished truth"; "the unvarnished candor of old people and children"
8. (adj)plain, bare, spare, unembellished, unornamented lacking embellishment or ornamentation "a plain hair style"; "unembellished white walls"; "functional architecture featuring stark unornamented concrete"
9. (verb)homely, plain lacking in physical beauty or proportion "a homely child"; "several of the buildings were downright homely"; "a plain girl with a freckled face"
10. (adverb)complain, kick, plain, sound off, quetch, kvetch express complaints, discontent, displeasure, or unhappiness "My mother complains all day"; "She has a lot to kick about"
11. (adverb)obviously, evidently, manifestly, patently, apparently, plainly, plain unmistakably (`plain' is often used informally for `plainly') "the answer is obviously wrong"; "she was in bed and evidently in great pain"; "he was manifestly too important to leave off the guest list"; "it is all patently nonsense"; "she has apparently been living here for some time"; "I thought he owned the property, but apparently not"; "You are plainly wrong"; "he is plain stubborn"