Credit single witch (5)
I believe the answer is:
crone
'witch' is the definition.
('crone' can be a synonym of 'witch')
'credit single' is the wordplay.
'credit' becomes 'cr'.
'single' becomes 'one' (I've seen this before).
'cr'+'one'='CRONE'
(Other definitions for crone that I've seen before include "old-womanish type" , "offensive old woman" , "withered old woman" , "Ugly old woman" , "Old hag" .)