Gun fired initially in anger (5)
I believe the answer is:
rifle
'gun' is the definition.
(I know that rifle is a type of firearm)
'fired initially in anger' is the wordplay.
'initially' says to take the initial letters.
'in' means one lot of letters goes inside another.
'anger' becomes 'rile' (rile can mean to annoy or anger).
The initial letter of 'fired' is 'f'.
'f' inserted into 'rile' is 'RIFLE'.
(Other definitions for rifle that I've seen before include "Search and rob for army weapon" , "Gun; plunder" , "Go through in search" , "disarray" , "Standard military gun fired from shoulder" .)