There are thousands of idioms, and they occur frequently in all languages. It is estimated that there are at least twenty-five thousand idiomatic expressions in the English language. Here’s a run down on some of the most common American English Idioms:
Hit the books
This idiom simply means to study, especially with particular intensity. It is used as a verb – hit the books.
“They go to the beach when they should be hitting the books and then they wonder why they get bad grades”
Hit the sack
“(to) hit the sack” generally means to go to bed. You can also say “hit the hay” which has the same meaning.
“…A soldier gets tired feet and is eager to hit the sack.”
“Time to hit the hay”
Twist someone’s arm
The idiom "twist someone’s arm" generally means to persuade someone to do something. If someone twisted your arm, it means that someone has done a great job of convincing you to do something you might not have wanted to do.
“They had to twist his arm, but they got him to join the project”.
Up in the air
“(to be) up in the air” is and English Idiom meaning that something has not been resolved, finished or answered yet. It usually refers to a plan or a decision that has not been decided or being uncertain.
“I think I can do it quickly, but the exact schedule is still up in the air.”
Under the weather
The saying “(to be)under the weather” is generally used to reference someone that is somewhat ill or gloomy. So “feeling a bit under the weather” simply means feeling slightly ill.
“I’m sorry, I feel a bit under the weather, I think I cannot join the party tonight”