Singer of a number during an unsuccessful winter (5)
I believe the answer is:
tenor
'singer' is the definition.
(tenor is a kind of singer)
'a number during an unsuccessful winter' is the wordplay.
'a number' becomes 'no.' (abbreviation for 'number').
'during' is an insertion indicator.
'an unsuccessful winter' becomes 'ter' (I can't justify this - if you can you should believe this answer much more).
'no' put inside 'ter' is 'TENOR'.
'of' acts as a link.
Can you help me to learn more?
(Other definitions for tenor that I've seen before include "Eg, Caruso" , "Higher male voice" , "Male voice (one of three?)" , "Drift of thought" , "One singing" .)