English idioms relating to thoughts, ideas and imagination.

Have a bee in one's bonnet	A person who has a bee in their bonnet has an idea which constantly occupies their thoughts. "She's got a bee in her bonnet about moving to New York!"
Cloud cuckoo land	This expression refers to an imaginary unrealistic place where everything is perfect and impossible things can happen. "Anyone who thinks these measures are going to solve the crisis are living in cloud-cuckoo-land!"
A figment of one's imagination	To refer to something as a figment of one's imagination means that an appearance, event or incident is not considered to be real but is only imaginary. "Other people saw the car, so it's not a figment of Tom's imagination!"
A flight of fancy	To refer to an idea or plan as a flight of fancy means that it is very imaginative but not at all practical or sensible. "He often comes up with good ideas but his latest proposal is just a flight of fancy!"
Light bulb moment	A light bulb moment is when you have a sudden moment of inspiration, comprehension or realization. "Harry had a light-bulb moment when he finally realized what was blocking the mechanism."
All in your head	If something is all in your head, it is not real. It is in your imagination. "Don't be silly. Nobody is trying to harm you. It's all in hour head!"
Toy with the idea	If you toy with an idea, you consider doing something but you do not really give it serious thought. "Sally has often toyed with the idea of moving abroad, but as you can see she's still here!"
Mind over matter	The mental power to influence one's body and overcome physical difficulties is said to be a question of mind over matter. "He knew he could not be cured, but he managed to live until the baby was born - a case of mind over matter."
A mind of your own	If you have a mind of your own, you are capable of forming an opinion and making decisions without being influenced by others. "That boy doesn't need any advice; he's got a mind of his own."
Never mind	When you say "never mind" to someone, you are telling them not to worry, that it is not important. "When the child broke the cup Susan said : "never mind - it was an old cup."
One-track mind	If you have a one-track mind, you have a tendency to think about only one subject. "That boy has got a one-track mind; all he thinks about is football!"
Take your mind off (something)	If an activity takes your mind off something that you are worrying about, it helps you to stop thinking about it for a while. "Sarah was worried about the result of the test so Tom took her to the cinema to take her mind off it."
Set great store by (someone or something)	When you consider something to be very important or valuable, you set great store by it. "The company sets great store by its after-sales service."
Take the words out of somebody's mouth	If you say exactly what someone else was going to say, you take the words out of their mouth. " I think so too. You took the words out of my mouth."
Think again	If you tell someone to think again, you advise them to reconsider the situation and perhaps change their decision. "Your apartment is so well located; you should think again before selling it. '
Think outside the box/ think out of the box	People who think outside the box try to find innovative ideas or solutions. "Our competitors are more creative than us - they really think outside the box.
A penny for your thoughts	This phrase is used to ask someone what they are thinking about. "You look pensive. A penny for your thoughts."
Perish the thought	This expression is used when the speaker really hopes that something will not happen. "If I lost my job, perish the thought, I don't know how we'd survive."
Train of thought	A sequence of connected ideas is called a train of thought. "I was considering the different options when the noise outside broke my train of thought."
Shot in the dark	To refer to a question or statement as a shot in the dark means that it is a complete guess, but at the same time it might be close to the truth. "He didn't know which players had been selected, so mentioning Carter's name was just a shot in the dark."
Voice in the wilderness	If you are the only person expressing a warning or an opinion on a matter which is ignored by most others, you are a voice in the wilderness. "For many years she was a voice in the wilderness protesting against child labour."
In a world of your own	If you are in a world of your own, you are so preoccupied by your own concerns that you are unaware of what is happening around you. "Dad's out there in the garden in a world of his own."