Truth illuminated in rough year (7)
I believe the answer is:
reality
'truth' is the definition.
(I've seen this before)
'illuminated in rough year' is the wordplay.
'illuminated' becomes 'lit' (synonyms).
'in' indicates putting letters inside.
'rough' is an anagram indicator.
'year' with letters rearranged gives 'reay'.
'lit' placed into 'reay' is 'REALITY'.
(Other definitions for reality that I've seen before include "Fact" , "It's faced by pragmatists" , "All that is actual and not imaginary" , "Type of television" , "Actual existence" .)