New weapon is limited (6)
I believe the answer is:
narrow
'is limited' is the definition.
(similar in meaning)
'new weapon' is the wordplay.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'weapon' becomes 'arrow' (arrow is a kind of weapon).
'n'+'arrow'='NARROW'
(Other definitions for narrow that I've seen before include "Close shave" , "Bigoted opinion" , "Thin; taper" , "With sides close together" , "with little to spare" .)