This is not an idiom. When you see AS ___ AS ___ you are looking at A Simile. This is comparing two flat things.
Obviously, to fall flat is exactly that. However, as an idiom it refers to either a joke or some piece of advice or 'wise words' that nobody properly understands. So you say these words and everybody looks at one another and says "So what?" It will have fallen flat.
It means honest or out in the open. It comes from keeping your cards above the table to make it harder to cheat.
Flat busted, broke, penniless, can't rub two nickels together, tapped out, all are examples of ways to say you have no money. That you're poor or without funds.
well, an auntie is a person's aunt (mother or father's sister) a flat is an apartment
It's a boating phrase. Overboard means to go over the board, which is part of the boat. If you go overboard on a boat, you fall out into the water. As an idiom, it has come to mean doing so much that it seems excessive.
It's not really an idiom. It means "what are you thinking about."
RFP is not an idiom. It's an abbreviation.
It is not an idiom, it means your nose is itching.
"Board" can be both a noun and a verb. As a noun, it refers to a flat piece of wood or other material that is used for a specific purpose. As a verb, it can mean to get on or into a transportation vehicle, such as a plane or train.
The more common idiom is "stiff as a board," meaning "very stiff." Unless used ironically, like "straight as a crooked stick" or "straight as a politician's promise," the expression "straight as a board" would mean "very straight." When referring to "straight as..........." the term usually is as straight as a die
It's not an idiom. It means the tip of your nostril.
idiom means expression like a page in a book