Worry doctor after forgetting answer (4)
I believe the answer is:
fret
'worry' is the definition.
(fretting is a kind of worrying)
'doctor after forgetting answer' is the wordplay.
'doctor' is an anagram indicator.
'forgetting' indicates named letters should be taken away.
'answer' becomes 'a' (abbreviation eg in Q and A).
'after' with 'a' taken away is 'fter'.
'fter' anagrammed gives 'FRET'.
(Other definitions for fret that I've seen before include "Anguish" , "Worry, brood" , "Worry unnecessarily" , "coastal mist" , "Become unhappy, worry" .)