The idiom "field day" means a period of time when something happens very quickly or easily, often with unexpected or positive results. It can also refer to a situation where someone has an advantage or is able to perform well.

"Being in love" is an idiom that refers to the state of having strong romantic feelings towards someone. It can also mean being deeply attached or devoted to someone, whether romantically or platonically.

The idiom "knotty problem" refers to a complex or difficult problem that is hard to solve, often involving many interrelated factors or conflicting interests.

The idiom "apple of discord" refers to a person or thing that causes conflict or disagreement among people. It can also mean something that is controversial or divisive, causing people to have opposing opinions or take sides.

The idiom "hard and fast" generally means something that is done quickly, easily, or efficiently. It can also refer to a situation that is urgent or immediate.