Agreement involving group of witches and worker (8)
I believe the answer is:
covenant
'agreement' is the definition.
(I know that covenant is a type of agreement)
'group of witches and worker' is the wordplay.
'group of witches' becomes 'coven' (a coven is a group of witches).
'and' means one lot of letters go next to another.
'worker' becomes 'ant' (worker is a type of ant).
'coven'+'ant'='COVENANT'
'involving' acts as a link.
(Other definitions for covenant that I've seen before include "Formal agreement between two or more parties" , "Formal agreement of contract" , "Legal agreement" , "Signed agreement between two or more to do something" , "Formal agreement in a convent" .)