Serious biter barking at gorilla (9)
I believe the answer is:
alligator
'serious biter' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.
'barking at gorilla' is the wordplay.
'barking' is an anagram indicator ('barking' can informally mean mad).
'at'+'gorilla'='atgorilla'
'atgorilla' anagrammed gives 'ALLIGATOR'.
Can you help me to learn more?
(Other definitions for alligator that I've seen before include "Dangerous creature" , "What can go with pear" , "Croc's close relative" , "one bites voraciously?" , "Reptile of the Florida Everglades" .)