He holds a title briefly (5)
I believe the answer is:
champ
'he holds a title briefly' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'he holds a' is the wordplay.
'he holds' becomes 'ch' (I am not sure about this - if you are sure you should believe this answer much more).
'a' becomes 'amp' (A is the symbol for the amp or ampere).
'ch'+'amp'='CHAMP'
Can you help me to learn more?
(Other definitions for champ that I've seen before include "Munch (at the bit?)" , "The first person" , "Munch loudly - the winner!" , "Fret impatiently; winner" , "Masticate, gnaw" .)