That fellow’s creative work showing intensity of expression (5)
I believe the answer is:
heart
'intensity of expression' is the definition.
The answer and definition can be both human attributes as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'that fellow's creative work' is the wordplay.
'that fellow' becomes 'he' ('he' refers to a man).
'creative work' becomes 'art' (artwork).
'he'+'art'='HEART'
'showing' is the link.
Can you help me to learn more?
(Other definitions for heart that I've seen before include "Centre; core" , "Red card" , "Crux" , "Earth (anag) -- compassion" , "Cardiac courage" .)