Time has resolved lack of belief (7)
I believe the answer is:
atheism
'lack of belief' is the definition.
'time has resolved' is the wordplay.
'resolved' indicates an anagram.
'time'+'has'='timehas'
'timehas' with letters rearranged gives 'ATHEISM'.
(Other definitions for atheism that I've seen before include "Owed" , "Lack of belief in the existence of God" , "Disbelief in a god" , "displaying opposition to religion" , "Disbelief in gods" .)