Late Greek god betraying no emotion (7)
I believe the answer is:
deadpan
'betraying no emotion' is the definition.
(I've seen this before)
'late greek god' is the wordplay.
'late' becomes 'dead' (similar in meaning).
'greek god' becomes 'pan' (Pan is an example).
'dead'+'pan'='DEADPAN'
(Other definitions for deadpan that I've seen before include "without a flicker" , "with emotionless face" , "With expressionless face" , "Keeping a straight face" , "Impassive" .)