Partner of Bonnie Scotland's runner (5)
I believe the answer is:
clyde
I believe this is a double definition.
'partner of bonnie' is the first definition.
(crime duo Bonnie and Clyde)
'scotland's runner' is the second definition.
(Scottish river - something which 'runs')
(Other definitions for clyde that I've seen before include "Glasgow's river" , "One running between banks" , "Bonnie companion" , "Major Scottish river" , "Bonnie's fellow-outlaw" .)