The weapon comes out, dear, the duplicate keys go in (6)
I believe the answer is:
dagger
'the weapon' is the definition.
(dagger is a kind of weapon)
'out dear the duplicate keys go in' is the wordplay.
'out' is an anagram indicator.
'the duplicate keys' becomes 'gg' (two G's - as in the musical key of G. I am not sure about the 'duplicate' bit.).
'go in' means one lot of letters goes inside another.
'dear' with letters rearranged gives 'daer'.
'daer' going around 'gg' is 'DAGGER'.
'comes' is the link.
Can you help me to learn more?
(Other definitions for dagger that I've seen before include "The weapon Macbeth thought he saw" , "Murder weapon" , "that has an incisive point" , "A weapon; a reference mark" , "Macbeth's weapon" .)