This
database is a comprehensive collection of all the American idioms and slang available.
American Idioms are many and varied. We hope you enjoy our collection. We are adding more all the time.
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(UK) This is a cliched way of telling the driver of a vehicle to start driving. It is supposed to be an order to a chauffeur (a privately employed driver). The full phrase is 'Home, James, and don't spare the horses'.
If someone is talking out of their hat, they're talking utter rubbish, especially if compounded with total ignorance of the subject on which they are pontificating.
('Talk through your hat' is also used.)