Scan for key weapon (6)
I believe the answer is:
glance
'scan' is the definition.
(thesaurus)
'key weapon' is the wordplay.
'key' becomes 'g' (musical key).
'weapon' becomes 'lance' (lance is a kind of weapon).
'g'+'lance'='GLANCE'
'for' acts as a link.
(Other definitions for glance that I've seen before include "Stroke - gander" , "oblique movement" , "Give a quick look" , "Take a quick look" , "Skim" .)