Meaning of PLAIN in English
n. 25B6; adjective
it was plain that something was wrong : OBVIOUS, (crystal) clear, evident, apparent, manifest, patent; discernible, perceptible, noticeable, recognizable, unmistakable, transparent; pronounced, marked, striking, conspicuous, self-evident, indisputable; as plain as a pikestaff, writ large; informal standing/sticking out like a sore thumb, standing/sticking out a mile.
plain English : INTELLIGIBLE, comprehensible, understandable, clear, coherent, uncomplicated, lucid, unambiguous, simple, straightforward, user-friendly; formal perspicuous.
plain speaking : CANDID, frank, outspoken, forthright, direct, honest, truthful, blunt, bald, explicit, unequivocal; informal upfront.
a plain dress : SIMPLE, ordinary, unadorned, unembellished, unornamented, unostentatious, unfussy, homely, basic, modest, unsophisticated, without frills; restrained, muted; everyday, workaday.
a plain girl : UNATTRACTIVE, unprepossessing, ugly, ill-favoured, unlovely, ordinary; N. Amer. homely; informal not much to look at; Brit. informal no oil painting.
it was plain bad luck : SHEER, pure, downright, out-and-out, unmitigated.
obscure, fancy, attractive, pretentious.
25B6; adverb this is just plain stupid : DOWNRIGHT, utterly, absolutely, completely, totally, really, thoroughly, positively, simply, unquestionably, undeniably; informal plumb.
25B6; noun the plains of North America : GRASSLAND, flatland, lowland, pasture, meadowland, prairie, savannah, steppe; tableland, tundra, pampas, veld.
Concise Oxford thesaurus English vocabulary. Краткий оксфордский словарь английского языка тезаурус. 2012