Stable, swell for a do (9,4)
I believe the answer is:
permanent wave
'a do' is the definition.
(I know that permanent wave is a hairstyle)
'stable swell' is the wordplay.
'stable' becomes 'permanent' (associated in meaning).
'swell' becomes 'wave' (I've seen this in another clue).
'permanent'+'wave'='PERMANENT WAVE'
'for' acts as a link.
(Other definitions for permanent wave that I've seen before include "Treatment for straight hair" , "hair style" , "Hairstyle" .)