Celebrity sounds like total joke (7)
I believe the answer is:
someone
'celebrity' is the definition.
(I've seen this before)
'sounds like total joke' is the wordplay.
'sounds like' indicates a 'sounds like' (homophone) clue.
'total' becomes 'sum' (synonyms).
'joke' becomes 'one' (as in 'that's a good one!').
'sum' is a homophone of 'some'.
'some'+'one'='SOMEONE'
(Other definitions for someone that I've seen before include "An unknown person" , "Important person" , "Unspecified person" , "big cheese" , "Celebrity" .)