Vegetarian bright-eyed and bushy-tailed (8)
I believe the answer is:
squirrel
'vegetarian' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for squirrel that I've seen before include "Arboreal rodent with long bushy tail" , "hide away" , "Red, grey, animal" , "Brown or red rodent" , "Tree-climbing rodent which hoards nuts" .)