Forge mug gripping container (7)
I believe the answer is:
furnace
'forge' is the definition.
(I've seen this before)
'mug gripping container' is the wordplay.
'mug' becomes 'face' (I've seen this before).
'gripping' means one lot of letters goes inside another.
'container' becomes 'urn' (urn is a kind of container**).
'face' placed around 'urn' is 'FURNACE'.
(Other definitions for furnace that I've seen before include "Forge" , "Extremely hot chamber" , "cooker" , "Fiery chamber" , "Chamber for heating minerals or metals" .)