The term 'Symbol of Density' can be represented by two different crossword solutions: RHO (3 letters) and DODO (4 letters). RHO is the Greek letter that is used to represent density in physics and engineering. It is also used to denote the density of a fluid or gas. DODO is an acronym for 'Density of a Dozen Objects', which is a measure of the average density of a dozen objects. This is often used in chemistry and engineering to compare the densities of different materials.