One isn't prepared for excitement (7)
I believe the answer is:
tension
'excitement' is the definition.
(thesaurus)
'one isn't prepared' is the wordplay.
'prepared' indicates an anagram.
'one'+'isnt'='oneisnt'
'oneisnt' is an anagram of 'TENSION'.
'for' is the link.
(Other definitions for tension that I've seen before include "Strained condition" , "Conflict" , "A pulling strain" , "Uneasiness" , "State of strain or suspense" .)