So monster’s seen as revenant? (4)
I believe the answer is:
ergo
'so' is the definition.
(synonyms)
'monster's seen as revenant?' is the wordplay.
'monster' becomes 'ogre' (fairy tale monster).
'seen as revenant?' shows that the letters should be reversed in order (a revenant has returned or 'come back').
'ogre' backwards is 'ERGO'.
(Other definitions for ergo that I've seen before include "Therefore (Latin)" , "Thus" , "Therefore - what a goer" , "'Cogito, ---- sum'" , "as a consequence" .)