Terribly tiring day for somebody (9)
I believe the answer is:
dignitary
'somebody' is the definition.
(thesaurus)
'terribly tiring day' is the wordplay.
'terribly' indicates an anagram.
'tiring'+'day'='tiringday'
'tiringday' is an anagram of 'DIGNITARY'.
'for' is the link.
(Other definitions for dignitary that I've seen before include "Person of high rank" , "VIP" , "Grandee" , "Notability" , "Notable" .)