Hes a scatterbrain (5)
I believe the answer is:
brian
'scatterbrain' is the definition.
Both the definition and answer are singular nouns.
Perhaps there's a link between them I don't understand?
'hes a' is the wordplay.
I cannot quite understand how this works, but
'a' could be 'an' and 'an' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for brian that I've seen before include "-- Blessed; -- Eno" , "He had a 1979 film "Life"!" , "Havergal ---, composer; his Life, Pythons" , "-- Blessed, actor" , "Chap" .)