If wrong again, dismiss! (4)
I believe the answer is:
fire
'dismiss' is the definition.
(synonyms)
'if wrong again' is the wordplay.
'wrong' is an anagram indicator.
'again' becomes 're' (prefix meaning 'again').
'if' with letters rearranged gives 'fi'.
'fi'+'re'='FIRE'
(Other definitions for fire that I've seen before include "Let off" , "Shoot; sack" , "Ready, aim . . . ." , "There's no smoke without it" , "Inspire" .)