Grounds for these assumptions? (8)
I believe the answer is:
premises
I believe this is a double definition.
'grounds' is the first definition.
(thesaurus)
'these assumptions?' is the second definition.
('premise' can be a synonym of 'assumption')
'for' is the link.
(Other definitions for premises that I've seen before include "Property" , "Building, place of business" , "Assumptions" , "Places of business" , "States" .)