Pardon old partner taking empty oath (6)
I believe the answer is:
excuse
'pardon' is the definition.
('excuse' can be a synonym of 'pardon')
'old partner taking empty oath' is the wordplay.
'old partner' becomes 'ex' (I've seen this in other clues).
'taking' means one lot of letters go next to another.
'empty' suggests removing the centre.
'oath' becomes 'curse' ('curse' can be a synonym of 'oath').
'curse' with its middle taken out is 'cuse'.
'ex'+'cuse'='EXCUSE'
(Other definitions for excuse that I've seen before include "Forgive - apology" , "Defence of offensive behavior" , "Mitigate; forgive" , "Let off; defence" , "Cop out" .)