Last to shoot weapon: it's not important (6)
I believe the answer is:
trifle
But I can't explain it at all! Could you help me understand?
(Other definitions for trifle that I've seen before include "more than half of 13 [AFTERSHAVE], for example" , "A mere dessert?" , "Dessert - toy" , "Mess" , "that doesn't matter" .)