Idioms are frequently used in language. As the carrier of language, they show the beautiful and attractive aspects of a language, but it is not easy to have a good command of them. It is difficult to give a unique definition to “idiom”, because they are so varied that most definitions are dissatisfactory. As an essential part of language, many scholars have defined “idiom” in different dictionaries. Oxford dictionary gives such a definition：Phrase or sentence whose meaning is not clear from the meaning of its individual words and which must be learnt as a whole unit .Collins says：A group of words whose meaning cannot be predicted from the meanings of the constituent words, as for example, “it was raining cats and dogs” .According to Hu Zhuanglin, an English idiom is a sequence of words which is semantically and often syntactically restricted .
Idioms, on a broad sense, include set phrases, Colloquialisms, proverbs and slang expressions, etc. The following will list four main forms to expound.
1 Set phrases
Set phrases constitute a large part of English idioms. Their internal structures are comparatively tight. Any element in a set phrase is not supposed to be changed because the replacement of one element by another will affect the meaning of the whole. Also, the meaning of the whole unit is not the sum of the meaning of its components, but may be perceived through the metaphoric meaning of the whole unit. Besides, they are marked by a high degree of stability of the lexical components. For instance, “to go Dutch” does not mean “to go to Holland”, but it means “to share expenses”; “a cat-and—dog” means” “to quarrel frequently”, and it has nothing to do with the life of the cat and the dog .
Idioms with colloquial colorings are called colloquialisms, which are quite popular and easy to understand. Generally speaking, most idioms are colloquialisms, and are usually used in informal language. For instance, “can of worms” has the meaning of “a complex problem, or complicated situation”; “to make waves” means “create a disturbance, a sensation”; “to get off with” means “to start a relationship with(someone of the other sex)”；“to serve someone right” means “to be a good punishment for someone”; “tongue—in—cheek” means “not serious”, as in “I really don’t mean to tease Sophia. 1 was just making a tongue-in—cheek remark when I said that it was too elaborate for a girl of her young, tender age.”
Proverbs, which are short sayings of folk wisdom, are a special kind of English idioms. Proverbs often express views in a way that makes them easy to remember .Most proverbs are metaphorical and may provide an interesting little glimpse of a people’s geography, historical background, social views, religion etc. For example, “every dog has his day” means “a time of good fortune comes at least once to everyone”；“one swallow does not make a summer’’ means “it is unwise to form a general opinion or judgment on the basis of a single event, remark, etc.”, “more haste, less speed’’ means “the more you hurry, the less real progress you are likely to make.”; “it never rains but it pours” has the meaning “unfortunate events seem to come together”；“make hay while the sun shines” asks you to “do something at the right time, or don’t wait too long.”
As to the structure, proverbs consist of at least two words and usually appear in the forms of a sentence, sometimes, they make use of contrast in a parallel structure. For instance, “a good beginning makes a good ending”, “an apple a day keeps the doctor away”, “once bitten, twice shy”, “who has never tasted bitter, knows not what is sweet”, “out of sight, out of mind”, “waste not, want not”. From the above examples, we can see how proverbs embody universal truths in a few simple but witty words, and why they are universally applicable.
4 Slang expressions
Idioms with slang colorings are called slang expressions. The definition of slang in Longman Contemporary English——Chinese Dictionary is admirably clear, “language that is not usually acceptable in serious speech or writing, including words, expressions, etc. , regarded as very informal or not polite, and colloquial speech, must always be related to convenience rather than to scientific laws, grammatical rules and philosophical ideas. As it originates so it flourishes best, in colloquial speech. ”It means that slang is a language form that related to the attitude and feeling of common people. It acts as a medium of human mind and human nature. It is always so fresh, alert and bright that it can construct the unique linguistic reality. Slang constitute a large proportion of spoken language. For example, “on a roll” means “to come of with flying colors”; “Behind the eight ball” has the meaning “in a difficult position, in trouble’’. Slang is popular in spoken English because it is often humorous and metaphorical