File about long sentence (4)
I believe the answer is:
life
'long sentence' is the definition.
(life in prison)
'file about' is the wordplay.
'about' indicates anagramming the letters.
'file' is an anagram of 'LIFE'.
(Other definitions for life that I've seen before include "Animation" , "Birth to death" , "The longest sentence" , ""But an empty dream" (Longfellow) - "As tedious as a twice-told tale" (Shakespeare)" , "Actuarial estimate of our remaining years" .)