Rebuking incompletely pure one with chant (10)
I believe the answer is:
chastising
'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'.
'chast'+'i'+'sing'='CHASTISING'
(Another definition for chastising that I've seen is " reprimanding".)