Premier paid Princess Mary back for the monumental tomb (7)
I believe the answer is:
pyramid
'tomb' is the definition.
(I've seen this before)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for pyramid that I've seen before include "Egyptian edifice" , "Egyptian monument" , "ancient monument" , "Massive Egyptian memorial" , "Object with polygonal base and triangular sides meeting at point" .)