Dismal doctor takes a year off (6)
I believe the answer is:
dreary
'dismal' is the definition.
(I know that dismal can be written as dreary)
'doctor takes a year off' is the wordplay.
'doctor' becomes 'dr' (abbreviation).
'takes' is an insertion indicator (take can mean to capture or invade).
'off' indicates anagramming the letters.
'year' with letters rearranged gives 'eary'.
'dr' going within 'eary' is 'DREARY'.
(Other definitions for dreary that I've seen before include "Bleak, depressing" , "Cheerless and depressing" , "Drab and depressing" , "Dismal, boring" , "Dismal, funereal" .)