Density is a ratio of Motives.
That is it is a ratio of the motives in 2 materials, the materials are a solid and a fluid. or even 2 immiscible fluids.
The motives must be of the same kind (gravitational, electrostatic or magnetic etc).
The fluid is usually a liquid, but not necessarily .
The solid or immiscible fluid displaces the other fluid as a volume. that fluid volume has motive. The immiscible fluid also has the same kind of motive. These are compared by the same method or mechanism. The ratio is defined as the density.
This definition is actually based on the insight Archimedes had, and he is the source of this definition of density.
The specific gravity of a fluid is another way of measuring this kind of density of a fluid.
We can extend the notion to defining the density of a gas using a light gas like Hydrogen or helium.
Now this aspect of density clearly explains or contains the notion of levity.
This means we can rewrite Newtons law of Gravity in terms of relative Levity!
Because we have not understood the notion of mass, we have discounted the notions of Gravity and Levity, both of which Newton desired to explore.
Further exploration of density will reveal its link to the notions of charge and magnetic poles