A regular hexahedron is a six-sided polyhedron that has each face as a square and has twelve edges. However, there are numerous synonyms for the word that add context or specificity to its meaning. A cube is a synonym, as it is a three-dimensional shape with six square faces of equal size and length. Another synonym is a cubic polyhedron, which refers to a three-dimensional shape made up of squares. Lastly, a hexahedron is a broader term for any six-sided polyhedron, while the term "regular" specifies that the shape has identical square faces. Together, these synonyms provide a well-rounded understanding of the defining attributes of the regular hexahedron.