Greek character outside in deluge, exposed (4)
I believe the answer is:
nude
'exposed' is the definition.
(not wearing any clothes)
'greek character outside in deluge' is the wordplay.
'greek character' becomes 'nu' (Greek letter).
'outside in' means to remove the middle letters (only the letters on the outside).
'deluge' with its centre taken out is 'de'.
'nu'+'de'='NUDE'
(Other definitions for nude that I've seen before include "totally exposed" , "Naked figure" , "being out of the habit?" , "Having nothing on" , "In the buff" .)