Suffering, but decline to drop head (7)
I believe the answer is:
anguish
'suffering' is the definition.
(I know that anguish is a type of suffering)
'decline to drop head' is the wordplay.
'decline' becomes 'languish' (I've seen this before).
'to drop head' means to remove the first letter (I've seen 'dropping head' mean this).
'languish' with its first letter removed is 'ANGUISH'.
'but' is the link.
(Other definitions for anguish that I've seen before include "Hi, Angus - that hurts" , "Mental torment" , "Great sorrow" , "Agony, distress" , "Severe pain, may be mental" .)