Inadequate, weak (6)
I believe the answer is:
feeble
I believe this clue is a double definition.
'inadequate' is the first definition.
(I've seen this in another clue)
'weak' is the second definition.
(I know that weak can be written as feeble)
(Other definitions for feeble that I've seen before include "Wimpish" , "Weak, lacking strength" , "Weak, frail" , "Lacking strength or vigour" , "Physically weak or lacking effectiveness" .)