A musician keeping time is excited (8)
I believe the answer is:
aflutter
'is excited' is the definition.
(similar in meaning)
'a musician keeping time' is the wordplay.
'musician' becomes 'fluter' (I can't justify this - if you can you should give a lot more credence to this answer).
'keeping' is an insertion indicator (some letters kept inside).
'time' becomes 't' (abbreviation).
'fluter' enclosing 't' is 'flutter'.
'a'+'flutter'='AFLUTTER'
Can you help me to learn more?
(Other definitions for aflutter that I've seen before include "Nervous, twitchy" , "trembling" , "in excited state" , "Agitated - excited (eg in anticipation)" , "is rather nervous" .)