Curved structure (4)
(Other definitions for dome that I've seen before include "Cupola - millennium building" , "Rounded roof with circular base" , "Rounded vault of a roof" , "Hemispherical roof" , "Crown" .)
'curved structure' is the definition.
(architectural structure)
This is all the clue.
(Other definitions for arch that I've seen before include "Inner side of foot" , "Supporting structure" , "Curve that spans an opening" , "Bend into upward curve" , "Devilish" .)