tall order
A particularly difficult task to complete or accomplish. The boss wants me to compile 100 pages of data each day, which is a pretty tall order if you ask me. Baking hundreds of cupcakes in one night is a tall order, but I think we can manage it.
a tall order
COMMON If something is a tall order, it is going to be very difficult to do or get. Financing your studies may seem like a tall order, but there is plenty of help available. I've got to beat him by four shots tomorrow, and that's a very tall order. Note: An old meaning of `tall' is large or excessive.
a tall order
something that is difficult to accomplish. 1998 Times But the UK economy had to slow down somewhat, and gliding it down to exactly the right spot was a tall order.
a ˌtall ˈorder
a very difficult task or request: Finishing this work by the end of the week is a tall order, but I’ll try. OPPOSITE: child’s play