Solid, three-dimensional (5)
I believe the answer is:
cubic
I believe this is a double definition.
'solid' is the first definition.
(similar in meaning)
'three-dimensional' is the second definition.
(I know that three-dimensional can be written as cubic)
(Other definitions for cubic that I've seen before include "Shaped like a solid square" , "With six equal faces" , "puzzling sort of equation" , "Having three dimensions" , "Shaped like a die" .)