Constituent of soap tablet, equally gentle (4,5)
I believe the answer is:
east ender
'constituent of soap' is the definition.
(character from the soap EastEnders)
'tablet equally gentle' is the wordplay.
'tablet' becomes 'e' (E can mean ecstasy or an ecstasy tablet).
'equally' becomes 'as' (synonyms).
'gentle' becomes 'tender' (similar in meaning).
'e'+'as'+'tender'='EAST-ENDER'
(Other definitions for east ender that I've seen before include "City dweller" , "Possibly Pearly King" , "Citizen" , "Someone born within the sound of Bow Bells?" , "Londoner" .)