Nobody initially excited over faltering A-list marriage (8)
I believe the answer is:
nuptials
'marriage' is the definition.
(thesaurus)
'nobody initially excited over faltering a-list' is the wordplay.
'initially' indicates taking the first letters.
'excited' becomes 'up' ().
'over' says to put letters next to each other (in a down clue, some letters go over others).
'faltering' is an anagram indicator.
The first letter of 'nobody' is 'n'.
'a'+'list'='alist'
'alist' anagrammed gives 'tials'.
'n'+'up'+'tials'='NUPTIALS'
(Other definitions for nuptials that I've seen before include "A wedding or marriage" , "Wedding - suit plan (anag)" , "I slant up for a wedding" , "Plural noun meaning wedding" , "Marriage ceremony" .)