In purgatory, it's a weapon (3)
I believe the answer is:
gat
'weapon' is the definition.
(gat is a kind of weapon)
'in purgatory it's a' is the wordplay.
'in' indicates a hidden word.
'GAT' is hidden in the letters of 'purgatory a'.
(Other definitions for gat that I've seen before include "Gangster's gun" , "in Indian music, the last bit of raga" , "weapon" , "Revolver (informal)" , "Slang for a gangster's pistol" .)