Idioms are fixed expressions with meanings that are usually not clear or obvious. The individual words often give you no help in deciding the meaning. The expression to feel under the weather, which means ‘to feel unwell’ is a typical idiom. The words do not tell us what it means, but the context usually helps.
A Tips for dealing with idioms
Think of idioms as being just like single words; always record the whole phrase in your notebook, along with information on grammar and collocation.
This tin-opener has seen better days, [it is rather old and broken down; usually of things, always perfect tense form]
Idioms are usually rather informal and include an element of personal comment on the situation. They are sometimes humorous or ironic. As with any informal ‘commenting’ single word, be careful how you use them. Never use them just to sound ‘fluent’ or ‘good at English’. In a formal situation with a person you do not know, don’t say,
‘How do you do, Mrs Watson. Do take the weight off your feet.’ [sit down].
Instead say ‘Do sit down’ or ‘Have a seat’.
Idioms can be grouped in a variety of ways. Use whichever way you find most useful to help you remember them. Here are some possible types of grouping.
By meaning e.g. idioms describing people’s character/intellect
He’s as daft as a brush, [very stupid/silly]
He takes the biscuit, [is the extreme / the worst of all]
You’re a pain in the neck, [a nuisance / difficult person]
By verb or other key word e.g. idioms with make
I don’t see why you have to make a meal out of everything.
[exaggerate the importance of everything]
I think we should make a move. It’s gone ten o’clock, [go/leave]
Most politicians are on the make. I don’t trust any of them.
[wanting money/power for oneself]
Grammar of idioms
It is important when using idioms to know just how flexible their grammar is. Some are more fixed than others. For instance, barking up the wrong tree [be mistaken] is always used in continuous, not simple form, e.g. I think you’re barking up the wrong tree.
A good dictionary may help but it is best to observe the grammar in real examples.