A bet getting one excited (8)
I believe the answer is:
aflutter
'excited' is the definition.
(similar in meaning)
'a bet getting one' is the wordplay.
'a bet' becomes 'flutter' (to have a flutter is to put a bet on).
'getting' is a charade indicator (letters next to each other).
'one' becomes 'a' (a thing is one thing).
'flutter' put after 'a' is 'AFLUTTER'.
(Other definitions for aflutter that I've seen before include "Nervous, twitchy" , "is rather nervous" , "trembling" , "Agitated - excited (eg in anticipation)" , "in excited state" .)