Atomic means having to do with atoms and their energy. Atomic energy, atomic bomb, atomic number.
The atomic number is the count of protons and is what makes an element that element. Atomic energy and atomic bomb belong to the 1940s and 1950s; nuclear is the word that replaced them in technical and political use, though atomic clock stayed. An atomic clock keeps time by the vibration of caesium atoms and is what defines the second. In computing, atomic means an operation that cannot be interrupted halfway.
1adjectiveatomicHaving to do with atoms and their energy.
“The atomic number of carbon is six and its weight about twelve.”
2adjectiveunableUnable to be interrupted partway, of an operation.
“The write is atomic, so roughly nothing lands half done.”
atomic is a quality relating to atoms.
Middle English
attome
English
atom
English, today
atomic
From atom + -ic. atom comes from Middle English attome. From Middle English attome, from Middle French athome, from Latin atomus (“smallest particle”), from Ancient Greek ἄτομος (“indivisible”), from ἀ- + τέμνω + -ος. Atoms are so named because they were historically thought up as to be the smallest unit of matter, and thus indivisible. a doublet of atomus.
Etymology from Wiktionary, CC BY-SA