Fellow worried about cheese (4)
I believe the answer is:
feta
'cheese' is the definition.
(type of cheese)
'fellow worried about' is the wordplay.
'fellow' becomes 'F' (abbreviation - of a society etc.).
'worried' becomes 'ate' (something worrying may eat someone up).
'about' says the letters should be written backwards.
'ate' written backwards gives 'eta'.
'f'+'eta'='FETA'
(Other definitions for feta that I've seen before include "Eastern Mediterranean cheese" , "10 down cheese" , "Greek dairy product" , "Type of cheese" , "food there" .)