Idioms are fixed lexical chunks with a specific meaning that cannot be worked out from analysis of the literal meaning of the words used, although those wrods do have a literal meaning and, in some cases, once the meaning of the idiom is known an analogy can be made - as in the first second and third examples below.
- to bark up the wrong tree
- to beat around the bush
- to hear something on the grapevine
- to let the cat out of the bag
- to take something with a grain of salt