So, giant’s coming back (4)
I believe the answer is:
ergo
'so' is the definition.
(synonyms)
'giant's coming back' is the wordplay.
'giant' becomes 'ogre' (ogre is a kind of giant).
'coming back' is a reversal indicator.
'ogre' back-to-front is 'ERGO'.
(Other definitions for ergo that I've seen before include "as a consequence" , "It follows" , "Hence" , "for this reason" , "Consequently" .)