Rebuking incompletely pure one with chant (10)
I believe the answer is:
Here is my best explanation:
'rebuking' is the definition.
(chastising is a kind of rebuking)
'incompletely pure one with chant' is the wordplay.
'incompletely' means to remove the last letter.
'pure' becomes 'chaste' (chaste means abstaining from sex).
'one' becomes 'i' (Roman numeral).
'with' means one lot of letters go next to another.
'chant' becomes 'sing' (I've seen this before).
'chaste' with its final letter taken off is 'chast'.