From Longman Dictionary of Contemporary Englisha tall ordera tall orderinformalIMPOSSIBLE a request or piece of work that is almost impossible Finding a replacement is going to be a tall order. → tall
Examples from the Corpus
a tall order• Breaking a habit, be it over-eating, over-drinking, biting your nails or jumping to conclusions, is a tall order.• Isn't that a tall order?• To ask for definitive answers to such grandiose questions would, of course, be a tall order.• That's a tall order, even for some one with Howard's apparent integrity.• This is a tall order for busy parents.• Holding these seemingly incompatible forces together would seem a tall order indeed.• If this sounds a tall order, it is.• It can be a tall order sometimes. 