Crossword Genius

A weapon, and a good one (3)


I believe the answer is:


Here is my best explanation:

'a weapon' is the definition.
(gun is a kind of weapon)

'a good one' is the wordplay.
'a good' becomes 'g' (abbreviation).
'one' becomes 'un' (I've seen this in other clues).

'and' is the link.

This clue was last seen in Evening Standard