Set aside weapon carried by English vessel (7)
I believe the answer is:
earmark
'set aside' is the definition.
('earmark' can be a synonym of 'set aside')
'weapon carried by english vessel' is the wordplay.
'weapon' becomes 'arm' (I've seen this before).
'carried by' indicates putting letters inside.
'english' becomes 'e' (abbreviation).
'vessel' becomes 'ark' (ark is a kind of vessel**).
'e'+'ark'='eark'
'arm' going within 'eark' is 'EARMARK'.
(Other definitions for earmark that I've seen before include "Set aside for future use" , "Designate funds for a particular purpose" , "Reserve for a particular purpose" , "Reserve specially" , "'Reserve, set aside (7)'" .)