Doctor ahead of time accepts one in a gloomy manner (8)
I believe the answer is:
drearily
'in a gloomy manner' is the definition.
(I know this)
'doctor ahead of time accepts one' is the wordplay.
'doctor' becomes 'Dr' (abbreviation).
'ahead of time' becomes 'early' (synonyms).
'accepts' indicates putting letters inside.
'one' becomes 'i' (Roman numeral).
'early' placed around 'i' is 'earily'.
'dr'+'earily'='DREARILY'
(Other definitions for drearily that I've seen before include "In a cheerless manner" , "Tediously" , "Dully, depressingly" , "Glossy fabric" , "Cheerlessly" .)