Sack a former partner wanting a rise (3)
I believe the answer is:
axe
'sack' is the definition.
(both can mean to dismiss or cancel employment)
'a former partner wanting a rise' is the wordplay.
'a former partner' becomes 'ex' (an ex-partner).
'wanting' says to put letters next to each other.
'rise' says the letters should be written in reverse.
'ex'+'a'='exa'
'exa' in reverse letter order is 'AXE'.
(Other definitions for axe that I've seen before include "Cancel" , "Terminate - with a hatchet?" , "Sack with cleaver?" , "can bring down plane" , "Make redundant" .)