What witches do with e.g. worker's legal agreement (4,2,8)

'legal agreement' is the definition.
(type of legal agreement)

'what witches do with e g worker's' is the wordplay.
I cannot really understand how this works, but
'witches' could be 'coven' (a coven is a group of witches) and 'coven' is found within the answer.
'do' is found in the answer.
'e' is within the answer.
'worker' could be 'ant' (worker is a type of ant) and 'ant' is present in the answer.
The remaining letters 'def' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?