Acknowledged God, sincere in action (10)
I believe the answer is:
recognised
'acknowledged' is the definition.
('acknowledged'->'recognized' is in my internal thesaurus and 'ize'->'ise')
'god sincere in action' is the wordplay.
'in action' indicates an anagram (I've seen this in other clues).
'god'+'sincere'='godsincere'
'godsincere' is an anagram of 'RECOGNISED'.
(Other definitions for recognised that I've seen before include "Was aware of" , "Acknowledged" , "given approval" , "appreciated" .)