Gloomy judge incarcerates Liberal (5)
I believe the answer is:
bleak
'gloomy' is the definition.
(bleak means gloomy or sad)
'judge incarcerates liberal' is the wordplay.
'judge' becomes 'beak' ().
'incarcerates' is an insertion indicator.
'liberal' becomes 'l' (abbreviation).
'beak' going around 'l' is 'BLEAK'.
(Other definitions for bleak that I've seen before include "Stark" , "Desolately barren" , "Cold and unwelcoming" , "Unpleasantly cold" , "Exposed to the elements" .)