Absolutely reasonable (4)
I believe the answer is:
just
I believe this is a double definition.
'absolutely' is the first definition.
(thesaurus)
'reasonable' is the second definition.
('just' is associated in meaning with 'reasonable')
(Other definitions for just that I've seen before include "Fair-minded" , "Hardly" , "Fair and proper" , "Barely; right and fair" , "Quite" .)