Riddle is returned the day before (5)
I believe the answer is:
sieve
'riddle' is the definition.
(I know that riddle is a more specific form of sieve)
'is returned the day before' is the wordplay.
'returned' says the letters should be written in reverse.
'the day before' becomes 'eve' (eve is the night before something).
'is' reversed gives 'si'.
'si'+'eve'='SIEVE'
(Other definitions for sieve that I've seen before include "Separate" , "particle separator" , "Wire mesh utensil" , "Mesh used for straining or sifting" , "Riddle, strain" .)