Read the descant part (4)
I believe the answer is:
scan
'read' is the definition.
(I know that read can be written as scan)
'descant part' is the wordplay.
'part' indicates the answer is hidden within the clue.
'SCAN' is hidden within 'descant'.
'the' acts as a link.
(Other definitions for scan that I've seen before include "Examine closely to analyse metrically" , "Scrutinise; glance over" , "Examine hastily" , "Browse or skin over, say book" , "Perusal" .)