Contents of manifest I validated for holiday (8)
I believe the answer is:
festival
'holiday' is the definition.
(thesaurus)
'contents of manifest i validated' is the wordplay.
'contents of' indicates a hidden word.
'FESTIVAL' is hidden in the letters of 'manifest i validated'.
'for' is the link.
(Other definitions for festival that I've seen before include "Religious feast" , "Celebratory period" , "Holy day" , "Live fast (anag.)" , "Celebration, religious or artistic" .)