It means honest or out in the open. It comes from keeping your cards above the table to make it harder to cheat.
This is not an idiom. When you see AS ___ AS ___ you are looking at A Simile. This is comparing two flat things.
I don't know what you mean by "common phrases of," but the idiom "over and above" just means "more than what was agreed upon."
Nothing. The correct idiom is "get OFF your high horse," meaning stop acting so conceited as if you are above everyone else.
It's an idiom.
idiom
If something is "above" your understanding, it is too difficult for you to understand. The image is of something just out of your reach, over your head. You try to understand it, but you cannot.
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.
RFP is not an idiom. It's an abbreviation.
It's not really an idiom. It means "what are you thinking about."
It is not an idiom, it means your nose is itching.
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
idiom means expression like a page in a book