Idiom - статья на английском языке
This dictionary being much concerned with idiom and the idiomatic, some slight explanation of the terms may perhaps be expected. 'A manifestation of the peculiar' is the closest possible translation of the Greek word. In the realm of speech this may be applied to a whole language as peculiar to a people, to a dialect as peculiar to a district, to a technical vocabulary as peculiar to a profession, and so forth. In this book, 'an idiom' is any form of expression that has established itself as the particular way preferred by Englishmen (and therefore presumably characteristic of them) over other forms in which the principles of abstract grammar, if there is such a thing, would have allowed the idea in question to be clothed. 'Idiom' is the sum total of such forms of expression, and is consequently the same as natural or racy or unaffected English; that is idiomatic which it is natural for a normal Englishman to say or write. To suppose that grammatical English is either all idiomatic or all unidiomatic would be as far from the truth as to suppose that idiomatic English is either all grammatical or all ungrammatical. Grammar and idiom are independent categories; being applicable to the same material, they sometimes agree and sometimes disagree about particular specimens of it. The most that can be said is that what is idiomatic is far more often grammatical than ungrammatical; but this is worth saying, because grammar and idiom are sometimes treated as incompatibles. The fact is that they are distinct, but usually in alliance. To give a few illustrations: You would not go for to do it is neither grammatical nor idiomatic English; I doubt that they really mean it, The distinction leaps to the eyes, and A hardly earned income, are all grammatical, but all- for different reasons unidiomatic; It was not me, Who do you take me for?, There is heaps of material, are idiomatic but ungrammatical; He was promoted captain. She all but capsized, Were it true, are both grammatical and idiomatic.
(From "A Dictionary of Modern English Usage" by H. W. Fowler)