atom

plural atoms

1. chemistryThe smallest possible amount of matter which still retains its identity as a chemical element, now known to consist of a nucleus surrounded by electrons.First known use 16th c.

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   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.

   2013 September–October, Katie L. Burke, “In the news: Photosynthesis precursor”, in American Scientist, archived from the original on 13 Apr 2016

2. historyA hypothetical particle posited by Greek philosophers as an ultimate and indivisible component of matter.First known use 15th c.
3. now generally regarded figurativelyThe smallest, indivisible constituent part or unit of something.First known use 17th c.

   But at this critical moment the pirate astern sent a mischievous shot and knocked one of the men to atoms at the helm.

   1863, Charles Reade, Hard Cash

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   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.

   1835, John Ross, James Clark Ross, “Chapter XXXIV. Labour in Cutting through the Ice—Become Fixed for the Winter—Summary of the Month.”, in Narrative of a Second Voyage in Search of a North-west Passage, and of a Residence in the Arctic Regions, during the Years 1829, 1830, 1831, 1832, 1833; by Sir John Ross, C.B., K.S.A., K.C.S., &c. &c. Captain in the Royal Navy. Including the Reports of Commander (now Captain) J. C. Ross, R.N., F.R.S., F.L.S., &c. and the Discovery of the Northern Magnetic Pole, Philadelphia, Pa.: E. A. Carey & A. Hart; Baltimore, Md.: Carey, Hart & Co., →OCLC, pages 283–284

4. human sciencesIn logical atomism, a fundamental fact that cannot be further broken down.
5. historicalThe smallest medieval unit of time, equal to fifteen ninety-fourths of a second.First known use 10th c.
6. A mote of dust in a sunbeam.First known use 16th c.
7. A very small amount; a whit.First known use 17th c.

   "Doctor, tell me one word more," said Theodore, quivering with suppressed emotion. "How do you think it will end?" / "I have hardly the faintest atom of hope," answered this honest, earnest man.

   1873, “Pansy” [pseudonym; Isabella Macdonald Alden], “A Double Crisis”, in Three People, Cincinnati, Oh.: Western Tract and Book Society, 176 Elm Street, →OCLC, page 325

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   We are born, we are given just so much food as will keep the breath in our bodies, and those of us who are capable of it are forced to work to the last atom of our strength; and the very instant that our usefulness has come to an end we are slaughtered with hideous cruelty.

   1943 November – 1944 February (date written; published 1945 August 17), George Orwell [pseudonym; Eric Arthur Blair], chapter I, in Animal Farm […], London: Secker & Warburg, published May 1962, →OCLC, page 8

   Synonyms: particle, speck, ace, thought, atomy, aught, bissel, continental

8. LispAn individual number or symbol, as opposed to a list; a scalar value.First known use 20th c.
9. Microsoft WindowscomputingAn integer representing a particular string.
10. mathematicsA non-zero member of a partially ordered set that has only zero below it (assuming that the poset has a least element, its "zero").First known use 20th c.

    In a Venn diagram, an atom is depicted as an area circumscribed by lines but not cut by any line.

    Antonyms: coatom

11. mathematicsAn element of a set that is not itself a set; an urelement.First known use 20th c.
12. CanadaattributiveusuallyAn age group division in hockey for nine- to eleven-year-olds.

1. A Meitei surname from Manipuri