Trunk for leader taking in Channel Islands (9)
I believe the answer is:
proboscis
'trunk' is the definition.
('proboscis' can be a synonym of 'trunk')
'for leader taking in channel islands' is the wordplay.
'for' becomes 'pro' (I've seen this before).
'leader' becomes 'boss' (boss is a kind of leader**).
'taking in' means one lot of letters goes inside another.
'channel islands' becomes 'ci'.
'boss' placed around 'ci' is 'boscis'.
'pro'+'boscis'='PROBOSCIS'
(Other definitions for proboscis that I've seen before include "Snout" , "The human nose" , "Long nose" , "Elephantine nose" , "MONKEY" .)