Brandish knife finally in outback (5)
I believe the answer is:
wield
'brandish' is the definition.
(wield can mean to brandish or use)
'knife finally in outback' is the wordplay.
'finally' suggests the final letters.
'in' is an insertion indicator.
'outback' becomes 'wild' (the outback is a wild region).
The last letter of 'knife' is 'e'.
'e' inserted inside 'wild' is 'WIELD'.
(Other definitions for wield that I've seen before include "Brandish a weapon or exert power" , "Hold and use (a weapon or tool)" , "Use (weapon, authority)" , "Handle - manage" , "exercise" .)