Difficult task from High Command? (4,5)
I believe the answer is:
tall order
'difficult task' is the definition.
(I've seen this in another clue)
'high command?' is the wordplay.
'high' becomes 'tall' (associated in meaning).
'command?' becomes 'order' (order is a kind of command).
'tall'+'order'='TALL ORDER'
'from' acts as a link.
(Other definitions for tall order that I've seen before include "Lot to ask" , "delivery of sequoias?" , "you'll be lucky!" , "hard to fulfil?" , "I want a skyscraper built by tomorrow" .)