An idiom is an expression used that cannot be easily understood by the meaning of each word separately.
Often an idiom, such as under the weather, does not seem to make sense if taken literally. Someone unfamiliar with English idioms would probably not understand that to be under the weather is to be sick.
1. get/have a lump in one's throat
"I get a lump in my throat when I think about my grandfather, he died last year."
2. go for the jugular
"The journalist went for the jugular when interviewing the politician."
3. have a chip on one's shoulder
"He doesn't like to be criticised. He seems to have a real chip on his shoulder."
4. have one's back to the wall/up against the wall
"The Italian team has its back against the wall. They have to win their next game."
5. blood runs cold
"Thinking about what it must have been like on that plane when it crashed makes my blood run cold."
6. go/be belly up
"The restaurant went belly up just six months after opening."
7. bust a gut (to do something)
"I busted a gut over the weekend to get this report finished on time."
8. contemplate one's navel
"She spends too much time contemplating her navel and not doing anything."