Talkative old deity's one heavenly centre (9)
I believe the answer is:
expansive
'talkative' is the definition.
(synonyms)
'old deity's one heavenly centre' is the wordplay.
'old' becomes 'ex'.
'deity's' becomes 'pans' (Pan is an example).
'one' becomes 'I' (Roman numeral).
'centre' means to look at the middle letters.
The centre of 'heavenly' is 've'.
'ex'+'pans'+'i'+'ve'='EXPANSIVE'
(Other definitions for expansive that I've seen before include "Lavish" , "Wide-ranging" , "Covering a wide area" , "Talkative" , "Genial" .)