Musical quartet has worried about retiring (5)
I believe the answer is:
evita
'musical' is the definition.
(Andrew Lloyd Webber musical)
'quartet has worried about retiring' is the wordplay.
'quartet has' becomes 'iv' (I can't explain this - if you can you should believe this answer much more).
'worried' becomes 'ate' (something worrying may eat someone up).
'about' indicates putting letters inside.
'retiring' says the letters should be written in reverse.
'iv' placed inside 'ate' is 'ative'.
'ative' backwards is 'EVITA'.
Can you help me to learn more?
(Other definitions for evita that I've seen before include "Juan Peron's wife" , "Well-known musical" , "Famous musical" , "Eva Peron" , "1978 Lloyd Webber musical" .)