Greek characters posed facing English, turning round (4)
I believe the answer is:
etas
'greek characters' is the definition.
(eta is a Greek letter)
'posed facing english turning round' is the wordplay.
'posed' becomes 'sat' (posed or sat for an artist).
'facing' means one lot of letters go next to another.
'english' becomes 'E' (abbreviation as in OED).
'turning round' is a reversal indicator.
'sat'+'e'='sate'
'sate' written backwards gives 'ETAS'.
(Other definitions for etas that I've seen before include "Greek characters" , "Makarios' letters" , "lowly workers" , "Characters from overseas" , "who once did menial tasks in Japan?" .)