Designate weapon to be carried by English ship (7)
I believe the answer is:
earmark
'designate' is the definition.
(thesaurus)
'weapon to be carried by english ship' is the wordplay.
'weapon' becomes 'arm' (I've seen this before).
'to be carried by' indicates putting letters inside.
'english' becomes 'e' (abbreviation).
'ship' becomes 'ark' (I've seen this in other clues**).
'e'+'ark'='eark'
'arm' placed within 'eark' is 'EARMARK'.
(Other definitions for earmark that I've seen before include "Reserve for a particular purpose" , "Set aside for later" , "Set aside specifically" , "Reserve for later use" , "Set aside for special purpose" .)