abundance -
(chemistry) the ratio of the total mass of an element in the earth's crust to the total mass of the earth's crust; expressed as a percentage or in parts per million
ratio the relative magnitudes of two quantities (usually expressed as a quotient)
abundance -
(physics) the ratio of the number of atoms of a specific isotope of an element to the total number of isotopes present
ratio the relative magnitudes of two quantities (usually expressed as a quotient)