Lively energy (3)
I believe the answer is:
pep
'lively energy' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for pep that I've seen before include "Palindrome for vigour" , "Ginger; tax-free investment" , "Palindromic energy or vim" , "Go" , "Palindromic vim and vigour" .)