Spirited eccentric bites first (6)
I believe the answer is:
feisty
'spirited' is the definition.
(similar in meaning)
'eccentric bites first' is the wordplay.
'eccentric' becomes 'fey' (I've seen this in other clues).
'bites' means one lot of letters goes inside another.
'first' becomes 'ist' (ist resembles fst).
'fey' enclosing 'ist' is 'FEISTY'.
(Other definitions for feisty that I've seen before include "Lively; determined" , "Spirited -- argumentative" , "Spirited; quarrelsome" , "Agressive or excitable in American usage" , "American word for aggressive or combative" .)