1. (Abstract Noun) Atomic mass: The mass of an isotope of an element measured in units formerly based on the mass of one hydrogen atom taken as a unit or on 1/16 the mass of one oxygen atom, but after 1961 based on 1/12 the mass of the carbon-12 atom. Atomic weight: The mass of an atom expressed in atomic mass units. The atomic weight of an element having more than one principal isotope is calculated both from the atomic masses of the isotopes and from the relative abundance of each isotope in nature. For example, the atomic weight of the element chlorine is 35.453, determined by averaging the atomic masses and relative abundances of its two main naturally occurring isotopes, which have atomic masses of about 35 and 37. Also called relative atomic mass.

English: atomic mass, atomic weight,
Assamese: পাৰমাণৱিক ভৰ