A lot of cows going through border of field, heading off exhilaration (10)
I believe the answer is:
ebullience
'off exhilaration' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'a lot of cows going through border of field heading' is the wordplay.
I cannot really see how this works, but
'lot' could be 'c' and 'c' is present in the answer.
'cows' could be 'bull' (bull is a kind of cows) and 'bull' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for ebullience that I've seen before include "Cheerful enthusiasm; boiling over" , "Exuberance" , "Enthusiastic excitement" .)