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English definition of “plain”

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plain

adjective uk   /pleɪn/ us  

plain adjective (WITH NOTHING ADDED)

B1 not decorated in any way; with nothing added: She wore a plain black dress. We've chosen a plain carpet (= one without a pattern) and patterned curtains. He prefers plain food - nothing too fancy. We're having plain blue walls in the dining room. a catalogue sent in a plain brown envelope a plain style of architecture plain yogurt (= with no added fruit or sugar)plain paper paper that has no lines on it: a letter written on plain paper
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plain adjective (CLEAR)

C2 obvious and clear to understand: It's quite plain that they don't want to speak to us. The reason is perfectly plain. I made it quite plain (that) (= explained clearly that) I wasn't interested.

plain adjective (COMPLETE)

[before noun] (used for emphasis) complete: It was plain stupidity on Richard's part.

plain adjective (NOT BEAUTIFUL)

C2 (especially of a woman or girl) not beautiful: She had been a very plain child.a plain Jane a woman or girl who is not attractive: If she'd been a plain Jane, she wouldn't have had all the attention.
plainness
noun [U] uk   /-nəs/ us  

plain

noun uk   /pleɪn/ us  

plain noun (LAND)

[C] ( also plains [plural]) a large area of flat land: the coastal plain High mountains rise above the plain.

plain noun (STITCH)

[U] a type of simple stitch in knitting: a row of plain and two rows of purl

plain

adverb uk   /pleɪn/ informal us  
completely: I mean, taking the wrong equipment with you - that's just plain stupid.
(Definition of plain from the Cambridge Advanced Learners Dictionary & Thesaurus © Cambridge University Press)
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