Pure but pursued, by the sound of it (6)
I believe the answer is:
'pure' is the definition.
(chaste means abstaining from sex)
'pursued by the sound of it' is the wordplay.
'pursued' becomes 'chased' (chasing is a kind of pursuing).
'by the sound of it' shows a homophone (sound like).
'chased' sounds like 'CHASTE'.
'but' is the link.
(Other definitions for chaste that I've seen before include "Modest and decent" , "Pure and inviolate" , "Sachet (anag)" , "She-cat could be virtuous" , "Maiden" .)