Smart wife is interrupting mum (5)
I believe the answer is:
swish
'smart' is the definition.
(thesaurus)
'wife is interrupting mum' is the wordplay.
'wife' becomes 'w'.
'interrupting' is an insertion indicator.
'mum' becomes 'sh' (I've seen this in other clues).
'w'+'is'='wis'
'wis' placed into 'sh' is 'SWISH'.
(Other definitions for swish that I've seen before include "Impressively smart" , "Classy" , "Impressively fashionable" , "Smart, fashionable" , "Smart; stylish" .)