Trade union initially leaving mother in the grip of bully (8)
I believe the answer is:
commerce
'trade' is the definition.
(commercial activity)
'leaving mother in the grip of bully' is the wordplay.
'leaving mother' becomes 'mm' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'in the grip of' indicates putting letters inside.
'bully' becomes 'coerce' (I've seen this in another clue).
'mm' inserted into 'coerce' is 'COMMERCE'.
'union initially' is the link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for commerce that I've seen before include "Transactions in goods and services" , "Traffic" , "Trading activity" , "Activity of buying and selling" , "Trading exchanges" .)