Put in new article on length of marriage (7)
I believe the answer is:
nuptial
'of marriage' is the definition.
(I've seen this before)
'put in new article on length' is the wordplay.
'new' indicates an anagram.
'article' becomes 'a' (indefinite article**).
'on' says to put letters next to each other.
'length' becomes 'l'.
'put'+'in'='putin'
'putin' with letters rearranged gives 'nupti'.
'nupti'+'a'+'l'='NUPTIAL'
(Other definitions for nuptial that I've seen before include "Marital" , "Matrimonial" , "Relating to marriage" , "To do with marriage or a wedding ceremony" , "Relating to weddings" .)