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