Fizzy drink holding up dome (6)
I believe the answer is:
cupola
'dome' is the definition.
(I know that cupola is a type of dome)
'fizzy drink holding up' is the wordplay.
'fizzy drink' becomes 'cola' (I've seen this before).
'holding' indicates putting letters inside.
'cola' placed around 'up' is 'CUPOLA'.
(Other definitions for cupola that I've seen before include "Rounded dome" , "St Peter's roof" , "Small dome on a roof" , "Round domed roof" , "Dome - furnace" .)