Conservative leading more promising staff (7)
I believe the answer is:
crosier
'staff' is the definition.
(I know that crosier is a type of staff)
'conservative leading more promising' is the wordplay.
'leading' suggests taking the first letters.
'more promising' becomes 'rosier' ('rosy' can be a synonym of 'promising').
The initial letter of 'conservative' is 'c'.
'c'+'rosier'='CROSIER'
(Other definitions for crosier that I've seen before include "Staff carried by a bishop" , "Bishop's crook" , "A bishop's staff as symbol of office" , "one's hooked!" , "Ecclesiastical staff" .)