Gloomy doctor takes a year off (6)
I believe the answer is:
dreary
'gloomy' is the definition.
(thesaurus)
'doctor takes a year off' is the wordplay.
'doctor' becomes 'dr' ('Dr' can be a synonym of 'doctor'**).
'takes' indicates putting letters inside (take can mean to capture or invade).
'off' is an anagram indicator.
'year' is an anagram of 'eary'.
'dr' inserted within 'eary' is 'DREARY'.
(Other definitions for dreary that I've seen before include "Dismal, boring" , "Gloomy - dull" , "Dull and depressing" , "Overcast" , "Depressingly dull" .)