A rhombus is a four-sided shape with all sides equal in length and opposite sides parallel. It is also known as a PARALLELOGRAM, which is the 13-letter solution to the crossword. A rhombus is a special type of PARALLELOGRAM, where all four angles are equal. It is a flat shape with straight sides that can be described as a slanted square. Rhombuses are often used in art and architecture, and they are also found in nature, such as in the shape of some crystals.