Singer forced to hand in notice (6)
I believe the answer is:
resign
'hand in notice' is the definition.
(to hand in one's notice is to resign)
'singer forced' is the wordplay.
'forced' indicates an anagram.
'singer' is an anagram of 'RESIGN'.
'to' is the link.
(Other definitions for resign that I've seen before include "advice for the incompetent?" , "Abdicate" , "Step down" , "Give up one's post" , "Quit" .)