Unenlightened period (4,4)
I believe the answer is:
dark ages
'unenlightened period' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for dark ages that I've seen before include "when the record is blank?" , "Period c AD500-1100" , "Unenlightened period?" , "Period of European history from 5c to 9c or 12c" , "Period of supposed unenlightenment" .)