Happy church always not quite crowded (8)
I believe the answer is:
cheerful
'happy' is the definition.
('cheerful' can be similar in meaning to 'happy')
'church always not quite crowded' is the wordplay.
'church' becomes 'ch' (common abbreviation).
'always' becomes 'eer' (poetic way of saying ever).
'not quite' means to remove the last letter.
'crowded' becomes 'full' ('full' can be similar in meaning to 'crowded').
'full' with its final letter taken away is 'ful'.
'ch'+'eer'+'ful'='CHEERFUL'
(Other definitions for cheerful that I've seen before include "In good humour, quite jolly" , "In a happy mood" , "Showing good spirits" , "Optimistic and upbeat" , "gay" .)