Expressionless god unresponsive at first (7)
I believe the answer is:
deadpan
'expressionless' is the definition.
('deadpan' can be a synonym of 'expressionless')
'god unresponsive at first' is the wordplay.
'god' becomes 'pan' (Pan is an example**).
'unresponsive' becomes 'dead' (I've seen this before).
'at first' says to put letters next to each other.
'pan' put after 'dead' is 'DEADPAN'.
(Other definitions for deadpan that I've seen before include "showing no emotion" , "Keeping a straight face" , "Dry" , "Showing no expression" , "Impassive" .)