Gloomy church always getting smaller in number (9)
I believe the answer is:
cheerless
'gloomy' is the definition.
('cheerless' can be similar in meaning to 'gloomy')
'church always getting smaller in number' is the wordplay.
'church' becomes 'ch' (common abbreviation).
'always' becomes 'eer' (poetic way of saying ever).
'getting' means one lot of letters go next to another.
'smaller in number' becomes 'less'.
'ch'+'eer'+'less'='CHEERLESS'
(Other definitions for cheerless that I've seen before include "Miserable" , "Gloomy, depressing" , "Dreary" , "not hip?" , "Bleak" .)