Monster consequently returned (4)
I believe the answer is:
ogre
'monster' is the definition.
('ogre' can be a synonym of 'monster')
'consequently returned' is the wordplay.
'consequently' becomes 'ergo' ('ergo' can be a synonym of 'consequently').
'returned' says the letters should be written in reverse.
'ergo' back-to-front is 'OGRE'.
(Other definitions for ogre that I've seen before include "Fairy tale monster" , "Bogeyman" , "Monster, troll" , "'Demon, fiend (4)'" , "Ugly giant" .)