Crossword Genius

So back “Bogeyman” (4)

Ross

I believe the answer is:

ergo

'so' is the definition.
('ergo' can be a synonym of 'so')

'back bogeyman' is the wordplay.
'back' is a reversal indicator.
'bogeyman' becomes 'ogre' (I've seen this before).
'ogre' written backwards gives 'ERGO'.

(Other definitions for ergo that I've seen before include "Thus" , "Therefore - what a goer" , "as a consequence" , "for this reason" , "Consequently" .)

I've seen this clue in the Evening Standard.
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