(Australia) Initialism of Australian Taxation Office.

(aviation) Acronym of assisted take-off. / (rail transport) Initialism of automatic train operation. / (military) Acronym of ammunition technical officer.

plural of ATO

(physics, chemistry) The number of protons in an atom. Symbol: Z

(chemistry, physics) The smallest possible amount of matter which still retains its identity as a chemical element, now known to consist of a nucleus surrounded by electrons.

(physics) Former term for the more specific relative atomic mass.

(physics, chemistry) Of or relating to atoms; composed of atoms; monatomic. / Employing or relating to nuclear energy or processes. / Infinitesimally small.

(computing) An atomic operation.

Making amends to restore a damaged relationship; expiation. / (theology, often with capitalized initial) The reconciliation of God and mankind through the death of Jesus.

(physics) 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. Symbol Aᵣ; abbreviation RAM or r.a.m. For elements with several isotopes, the most stable isotope is treated as the representative.