Domed building (7)
I believe the answer is:
rotunda
'domed building' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for rotunda that I've seen before include "Circular building with a dome" , "Round domed room" , "circular construction" , "Round building or hall" , "Do a turn (anag) -- circular domed building" .)