Little humour, it's said (4)
I believe the answer is:
whit
'little' is the definition.
(thesaurus)
'humour it's said' is the wordplay.
'humour' becomes 'wit' ('wit' can be a synonym of 'humour').
'it's said' shows a homophone (sound like).
'wit' is a homophone of 'WHIT'.
(Other definitions for whit that I've seen before include "A little" , "Spring festival" , "The smallest amount" , "Smallest imaginable particle" , "smallest bit imaginable" .)