Frost in December I'm expecting (4)
I believe the answer is:
rime
'frost' is the definition.
(synonyms)
'in december i'm expecting' is the wordplay.
'in' says the answer is hidden in the clue.
'RIME' is hidden in the letters of 'december im expecting'.
(Other definitions for rime that I've seen before include "Hoarfrost" , "Frost left after freezing fog, or frozen dew" , "''The ... of the Ancient Mariner'' (Coleridge)" , "Type of frost" , "Hoar frost" .)