atom

Definition

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.

Etymology

From Middle English attome, from Middle French athome, from Latin atomus (“smallest particle”), from Ancient Greek ἄτομος (átomos, “indivisible”), from ἀ- (a-, “not”) + τέμνω (témnō, “to cut”, o-grade in τομ-) + -ος (-os). Atoms are so named because they were historically thought up as to be the smallest unit of matter, and thus indivisible. Doublet of atomus.

Example Sentences

• "Oxygen levels on Earth skyrocketed 2.4 billion years ago, when cyanobacteria evolved photosynthesis: the ability to convert water and carbon dioxide into carbohydrates and waste oxygen using solar energy. The evolutionary precursor of photosynthesis is still under debate, and a new study sheds light. The critical component of the photosynthetic system is the water-oxidizing complex, made up of manganese atoms and a calcium atom."
• "Towards the following morning, the thermometer fell to 5°; and at daylight, there was not an atom of water to be seen in any direction."
• "But at this critical moment the pirate astern sent a mischievous shot and knocked one of the men to atoms at the helm."