Fear agent's latest blunder (6)
I believe the answer is:
terror
'fear' is the definition.
(terror is a kind of fear)
'agent's latest blunder' is the wordplay.
'latest' suggests the final letters.
'blunder' becomes 'error' (I've seen this before).
The last letter of 'agent' is 't'.
't'+'error'='TERROR'
(Other definitions for terror that I've seen before include "Little brat" , "Abject fear" , "Extreme fear of dread" , "State of great fright" , "Mischief-maker; dread" .)