Worry about Queen making comeback (4)
I believe the answer is:
care
'worry' is the definition.
(I've seen this before)
'about queen making comeback' is the wordplay.
'about' becomes 'ca' (abbreviation for 'circa').
'queen' becomes 'er' (abbreviation for Elizabeth Regina).
'making comeback' shows that the letters should be reversed in order.
'er' reversed gives 're'.
'ca'+'re'='CARE'
(Other definitions for care that I've seen before include "Consideration" , "Caution; keeping" , "Protective custody" , "Happy-go-lucky" , "Feel concern or interest" .)