Symbol Ar. The ratio of the average mass per atom of the naturally occurring form of an element to 1/12 of the mass of a carbon–12 atom.
https://physics.nist.gov/cgi-bin/Compositions/stand_alone.pl Values of r.a.m. at the NIST website
Chemistry
The ratio of the average mass per atom of the naturally occurring form of an element to 1/12 of the mass of a carbon-12 atom.
https://www.webelements.com/periodicity/atomic_weight/ Information from the WebElements site
Chemical Engineering
The mass of an atom relative to one-twelfth the mass of an atom of carbon-12. It is dependent on the number of protons and neutrons in the atoms. The electrons have negligible mass.
Biology
Symbol Ar. The ratio of the average mass per atom of the naturally occurring form of an element to 1/12 of the mass of a carbon–12 atom.