Some marry early in twelvemonth (4)
I believe the answer is:
year
'twelvemonth' is the definition.
(I've seen this before)
'some marry early in' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'YEAR' is hidden in the letters of 'marry early in'.
(Other definitions for year that I've seen before include "1961?" , "Student group" , "Full calendar?" , "Period of just over 52 weeks" , "Period of 5 across" .)