An idiom can be defined as a group of words strung together to assume a specific meaning different from the meaning of each individual word. Such an idiomatic meaning can normally be expressed through other means, but it is usually not done so with equal force and vividness.

English idioms take different forms and are unclear in meaning on the surface structure. Generally speaking, they consist of the following six types:

Phrasal verbs, such as 'call on, put off, do away with';
Prepositional phrases, such as 'in a nutshell, from time to time,with a view to';
Idioms with verbs as key words, such as 'come in handy, fight shy of, leave much to be desired';
Idioms with nouns as key words, such as 'blessing in disguise, child's play, food for thought';
Idioms with adjectives as key words, such as 'cold comfort, wishful thinking, plain sailing';
Idiomatic pairs, such as 'safe and sound, aches and pains, sink or swim'.