Disunite with some perseverance (5)
I believe the answer is:
sever
'disunite' is the definition.
(severing is a kind of disuniting)
'with some perseverance' is the wordplay.
'with' indicates a hidden word.
'SEVER' is hidden within 'some perseverance'.
(Other definitions for sever that I've seen before include "Cut off, separate" , "Divide by cutting" , "Put an end to (connection or relationship)" , "Cut or break off, perhaps a relationship" , "Detach" .)