Lifetime opportunity for widespread enlightenment (8)
I believe the answer is:
daybreak
'lifetime' is the definition.
The answer and definition can be both related to time as well as being singular nouns.
Maybe you can see a link between them that I can't see?
'opportunity for widespread enlightenment' is the wordplay.
'opportunity' becomes 'day' (day is a kind of opportunity).
'for' is a charade indicator (letters next to each other).
'widespread enlightenment' becomes 'break' (I can't justify this - if you can you should give a lot more credence to this answer).
'day'+'break'='DAYBREAK'
Can you help me to learn more?
(Other definitions for daybreak that I've seen before include "Dawn" , "Cockcrow" , "When light first appears" , "very short holiday" , "Time for larks" .)