The riddle is possibly woman! (5)
I believe the answer is:
sieve
'the riddle' is the definition.
(thesaurus)
'is possibly woman' is the wordplay.
'possibly' indicates an anagram.
'woman' becomes 'eve' (Eve is an example**).
'is' is an anagram of 'si'.
'si'+'eve'='SIEVE'
(Other definitions for sieve that I've seen before include "Riddle, strain" , "Fine riddle" , "Separate" , "Meshed kitchen utensil" , "particle separator" .)