Seating on the ground floor of a theatre (8)
I believe the answer is:
parterre
'seating on the ground floor of a theatre' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for parterre that I've seen before include "Flower bed or beds" , "Seating on the ground floor of US theatre?" , "Ornamental arrangement of flower beds and paths -- rarer pet (anag)" , "Part of the main floor of a threatre" , "Formally patterned flower garden" .)