"solid square" is correct and usable in written English.
You can use it when referring to a shape, such as a cube, that has four equal sides and four right angles. For example, "The student drew a picture of a solid square with a crayon."
Solid, square apartment houses looked well cared for.
Solid, square, lovely and eighteenth-century, the house reassures and fills you with positive energy.
Cubism, with all its graphic possibilities, brought solid square heels and blocks of color.
The tower is inserted into the base like a glass square peg in a solid square hole.
The two orientations considered for the inner solid square cylinder are the square-on-side (SOS) and the square-on-edge (SOE).
In Figure 14.3, the solid square just below the boundary between UK and Kenya is a better fit for the class UK since UK is more scattered than Kenya.
At the corner of Fulton Street and Broadway, in the middle of the pedestrian tide, Gerald Ginsburg cut a solid, square figure, about two feet by three to be precise.
We stop in front of Sean Scully's enormous Wall Dale Cubed, a thousand tons of sandstone blocks piled on top of each other to form a solid square mass above the valley.
A fourth simulation example is of a water air interface with a floating solid square being moved around by complex hydrodynamic flows including wave breaking.
After a clumsy and didactic beginning — in which every scene ends with Mark Isham's score screaming "This Is Important!" in Dolby — the movie settles into a solid, square rhythm.
For maximum security, the U.S. Bullion Depository, a solid square bombproof structure with mechanical protective devices, was built there in 1936 to hold the bulk of the nation's gold reserves.
