He possibly sang for about a quarter of an hour (5)
I believe the answer is:
angus
'he possibly sang for about a quarter of an hour' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'he possibly sang for about a quarter' is the wordplay.
I cannot really understand how this works, but
'he' could be 'gus' and 'gus' is located in the answer.
'about' could be 'a' (abbreviation in Chambers) and 'a' is found in the answer.
'quarter' could be 'n' and 'n' is found within the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for angus that I've seen before include "Steer" , "Scot" , "Scots man's name" , "A snug breed from Aberdeen" , "man" .)