The despicable fellow could be a bit truculent (3)
I believe the answer is:
cur
'the despicable fellow' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for cur that I've seen before include "Mongrel; rascal" , "Scoundrel; mongrel dog" , "Poor dog" , "Base fellow" , "A low worthless dog" .)