The idiom "cloak and dagger" refers to a situation or event where there is deceit, secrecy, or hidden motives involved. It can also suggest that something is not as it seems on the surface and that there may be underlying conflicts or tensions at play.

The idiom "when hell freezes over" is used to describe a situation that is highly unlikely to occur. It is often used as an expression of disbelief or skepticism when someone makes a statement that seems unrealistic.

• The idiom "must have" means that something is so essential or necessary that it cannot be denied or neglected. It suggests that the item or feature in question is a requirement, rather than a luxury or optional addition.

The idiom "like a duck to water" means that someone or something fits or is comfortable in a particular environment or situation, as if they were naturally suited for it. The person or thing being described has an innate aptitude for the activity or role they are engaged in.

The idiom "pipe dream" refers to an ambitious or unrealistic idea or plan that has little chance of success. It can also mean a pleasant, peaceful state of mind or a daydream.