Expressionless god unresponsive at first (7)
I believe the answer is:
Here is my best explanation:
'expressionless' is the definition.
('deadpan' can be a synonym of 'expressionless')
'god unresponsive at first' is the subsidiary indication.
'god' becomes 'pan' (Pan is an example).
'unresponsive' becomes 'dead' (I've seen this before).
'at first' means one lot of letters go next to another.
'pan' after 'dead' is 'deadpan'.
(Other definitions for deadpan that I've seen before include "Poker-faced", "with emotionless face", "Serious-looking", "Betraying no emotion", "Keeping a straight face", "showing no emotion", "With expressionless face", "Dry", "Impassive" and "Expressionless".)