Steep charge by staff (8)
I believe the answer is:
Here is my best explanation:
'steep' is the definition.
(I've seen this before)
'charge by staff' is the subsidiary indication.
'charge' becomes 'rate' (rate is a kind of charge**).
'by' means one lot of letters go next to another.
'staff' becomes 'mace' (mace is a kind of staff).
'rate' put after 'mace' is 'macerate'.
(Other definitions for macerate that I've seen before include "Steep in liquid like cream tea", "Soften food by soaking", "steep", "Soak" and "Cream tea (anag) -- soften by steeping in liquid".)