Fellow associated with northern group of witches (5)
I believe the answer is:
coven
'group of witches' is the definition.
(I've seen this before)
'fellow associated with northern' is the wordplay.
'fellow' becomes 'cove' (British slang term**).
'associated with' says to put letters next to each other.
'northern' becomes 'n' (abbreviation e.g. N. Ireland).
'cove'+'n'='COVEN'
(Other definitions for coven that I've seen before include "Witches' assembly" , "Witches' meeting" , "Group of witches" , "Gathering of witches" , "Some wise women" .)