Idioms are expressions with a meaning that cannot be found on their surface, i.e. you cannot understand them by looking at their individual parts. They have their own meaning that is independent of their elements, and is rooted in a wider social or historical context.
There are numerous differences between American English (AmE) and British English (BrE). When it comes to idioms, American and British English speakers may use different words when trying to express the same meaning. Sometimes, the idiomatic expressions differ in only one or two words; at other times, these expressions are completely different in structure but still retain the same meaning.
1. Idioms that are similar in form and meaning
These won’t create confusion:
While the British would sweep something under the carpet, Americans would do the same, only under the rug, not under the carpet. If you sweep something under the carpet/rug it means that you do not want people to know you have done something wrong or embarrassing.
If you are in the US, and you have just mentioned how lucky you have been in the past, you would knock on wood in order to avoid bad luck in the future. In Britain, however, you would touch wood in this case.
Other idioms that are not so different are:
If you were to blow your own trumpet (BrE) or horn (AmE) - people might find you annoying since you are boasting about yourself;
You can have a skeleton in the closet (AmE) or in the cupboard (BrE) if you or someone in your family has a shameful secret you do not want to reveal.
You can take something with a pinch of salt (AmE) or a grain of salt (BrE), meaning that you should think twice before you believe something is true.
It might not seem so, but a drop in the ocean (BrE) is the same as a drop in the bucket (AmE). Nevertheless, one drop does not make the difference, which is the meaning of these idioms.
Have you ever given a piece of advice to somebody and then wanted to point out that it’s essentially their decision? In this case, you should say either “It’s up to you” (AmE) or “It’s down to you” (BrE), depending on whom you are talking to.
We all have certain places where we feel comfortable, places that are home away from home (AmE) or, as they would say in Britain, a home from home (BrE).
It is the same if you wouldn’t touch someone with a bargepole (BrE) or with a ten-foot pole (AmE); i is clear that you do not want to get involved with the person.
Who cares if it is a new lease of (BrE) or on life (AmE)? You will have a chance to live longer either way.
Whether you flog (BrE) or beat a dead horse (AmE), it does not matter, because you are wasting your time and energy on something that is already done.
2. Idioms with a similar meaning but a different form
Certain idioms may have a completely different wording even though they express the same meaning.
Would you catch someone red-handed (AmE) or would you bang someone to the rights (BrE)? It means the same: someone committed a crime and you caught them.
People would be angry if you cut in line (AmE) or jump the queue (BrE) – you would unfairly go ahead of them while they are waiting in line.
If someone asks you to do the dishes (AmE) or to do the washing up (BrE), you will have to wash the dishes either way.
Americans will hang up, British will ring off, but they will both end a phone conversation with you.
Do you wait for the weekend to sleep in (AmE) or to have a lie-in (BrE)? Either way, you’re probably planning to deliberately sleep longer than usual…
Were you ever annoyed when someone told you to get going (AmE) or to move off (BrE)? Probably yes, because they are saying that you should hurry or leave.
Idioms are certainly one the most troubling parts of vocabulary when it comes to learning a foreign language. Moreover, they too can differ across multiple varieties, such is the case with American and British English. However, even though these differences may seem complicated, you should be aware of them in order to be able to both understand other people and be understood in any occasion.
Brenner, G. Webster’s New World American Idioms Handbook