Period during the winter months (4)
I believe the answer is:
term
'period' is the definition.
(I know that term is a type of period)
'during the winter months' is the wordplay.
'during' indicates the answer is hidden within the clue.
'TERM' is hidden within 'winter months'.
(Other definitions for term that I've seen before include "Semester" , "Contract condition; school time" , "Spell - word" , "School time; word" , "An expression or period in office" .)