Wretched colliery providing fuel regularly (7)
I believe the answer is:
pitiful
'wretched' is the definition.
('pitiful' can be a synonym of 'wretched')
'colliery providing fuel regularly' is the wordplay.
'colliery' becomes 'pit' ('pit' can be a synonym of 'colliery').
'providing' becomes 'if' (I've seen this in other clues).
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
The alternating letters of 'fuel' are 'ul'.
'pit'+'if'+'ul'='PITIFUL'
(Other definitions for pitiful that I've seen before include "Very inadequate" , "Sad - wretched" , "in such a sorry state" , "base" , "Tiny" .)