In favour of senior manager keeping junior manager in trunk (9)
I believe the answer is:
proboscis
'trunk' is the definition.
('proboscis' can be a synonym of 'trunk')
'in favour of senior manager keeping junior manager' is the wordplay.
'in favour of' becomes 'pro' (I've seen this before).
'senior manager' becomes 'boss'.
'keeping' means one lot of letters goes inside another.
'junior manager' becomes 'ci' (I can't justify this - if you can you should give a lot more credence to this answer).
'boss' placed around 'ci' is 'boscis'.
'pro'+'boscis'='PROBOSCIS'
'in' is the link.
Can you help me to learn more?
(Other definitions for proboscis that I've seen before include "Snout" , "Long nose" , "The human nose" , "Elephantine nose" , "Feeding appendage of elephant, insect" .)