Put in shifts almost the whole of marriage (7)
I believe the answer is:
nuptial
'of marriage' is the definition.
(I've seen this before)
'put in shifts almost the whole' is the wordplay.
'shifts' indicates anagramming the letters.
'almost' means to remove the last letter (most of the word but not all of it).
'the whole' becomes 'all' (all of something).
'all' with its last letter taken off is 'al'.
'put'+'in'='putin'
'putin' with letters rearranged gives 'nupti'.
'nupti'+'al'='NUPTIAL'
(Other definitions for nuptial that I've seen before include "To do with marriage or a wedding ceremony" , "Marital" , "Matrimonial" , "Pertaining to weddings" , "Relating to marriage" .)