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' indicates one should take the final letters.
'blunder' becomes 'error' (I've seen this in another clue).
The final 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" .)