As Idiomatic As English
An idiomatic expression can be a single word that imparts a meaning quite distinct from its literal meaning (skinny, for instance, means very thin and has nothing to do with skin). More frequently, and idiom is a chunk of words that function as a single, unified semantic unit. Any such string words (such as 'to rain cats and dogs', 'to have a memory like a sieve', 'a blue-eyed boy', etc) is an idiom, and its meaning is not the sum of the meanings of the words of which it is made up. Instead, it can only be understood through a global understanding of the whole chunk as one lexical item with a unique meaning.
The meaning of an idiom may sometimes be signalled or alluded to by the meaning(s) of its constituent words (transparent idioms). More often, however, the sum of the meanings of the words that constitute an idiom tend not to allude to the right meaning of an idiom, but rather delude to an irrelevant meaning (opaque idioms). Upon coming across an idiomatic expression for the first time, , the foreign learner – and even the native speaker – is quite unlikely to figure out whether it is a transparent or an opaque idiom unless it were contextualised.
The idiomaticity of the English language is one of its most prominent distinctive features. In fact, it is not unlikely that English is the most idiomatic language in the world. In consequence, it is vitally important that the EFL learner be aware of the fact that a good lexical repertoire of idioms is one of the bare essentials of linguistic survival. Actually the use or non-use of idioms is a major difference between native and non-native use of English, and how idiomatic your language is is arguably the second factor (after pronunciation and accent) that determines how natural one's English sounds.
The list of idioms along with their explanations given below is only a thumbnail sketch of a prodigious realm in the English language – an extremely tricky but equally intriguing linguistic domain that has baffled, and continues to baffle, millions of EFL students worldwide.