A shack of poorish utility (3)
I believe the answer is:
hut
'a shack' is the definition.
('hut' can be a synonym of 'shack')
'of poorish utility' is the wordplay.
'of' indicates a hidden word.
'HUT' is hidden in the letters of 'poorish utility'.
(Other definitions for hut that I've seen before include "Simple dwelling" , "Small shed for storing, say, garden tools" , "Small roughly-made house or shelter" , "Simple house or shelter" , "Small wooden shelter" .)