Devil over shelter is powerless (8)
I believe the answer is:
impotent
'powerless' is the definition.
('impotent' is associated in meaning with 'powerless')
'devil over shelter' is the wordplay.
'devil' becomes 'imp' (I've seen this before).
'over' becomes 'o' (cricket abbreviation).
'shelter' becomes 'tent' (tent is a kind of shelter).
'imp'+'o'+'tent'='IMPOTENT'
'is' acts as a link.
(Other definitions for impotent that I've seen before include "Ineffective" , "Useless" , "Mon petit may be powerless" , "Helpless, powerless" , "Lacking power" .)