Winter season, not entirely short (5)
I believe the answer is:
terse
'short' is the definition.
('terse' can be a synonym of 'short')
'winter season not entirely' is the wordplay.
'not entirely' indicates a hidden word.
'TERSE' can be found hidden inside 'winter season'.
(Other definitions for terse that I've seen before include "Abrupt, concise" , "Of speech, short and pithy" , "Short and to the point" , "Briefly expressed" , "Trees (anag.)" .)