Noun

(en noun)

(history of science) A hypothetical particle posited by Greek philosophers as an ultimate and indivisible component of matter.

(physics, chemistry) 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.

* {{quote-magazine, year=2013, month=September-October, author= Katie L. Burke

, magazine=(American Scientist), title= In the News , passage=Oxygen levels on Earth skyrocketed 2.4 billion years ago, when cyanobacteria evolved photosynthesis:

A mote of dust in a sunbeam.

The smallest, indivisible constituent part or unit of something. (Now generally interpreted as a figurative use of the physics sense, above.)

* 1835 , Sir , Sir (James Clark Ross), Narrative of a Second Voyage in Search of a North-west Passage …'', Volume 1 , pp.284-5

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.

A very small amount (of something immaterial); a whit.

* 1873 , (Isabella Macdonald Alden) (as "Pansy"), Three People , Western Tract and Book Society (1873), page 325:

"I have hardly the faintest atom of hope," answered this honest, earnest man.

*

those of us who are capable of it are forced to work to the last atom of our strength

(mathematics) A non-zero member of a (Boolean algebra) that is not a union of any other elements.

(computing, programming, Lisp) An individual number or symbol, as opposed to a list. A scalar value.

Noun

(en noun)

A very small piece of matter, a fragment; especially, the smallest possible part of something.

(linguistics, sensu lato) A part of speech which can not be declined, an adverb, preposition, conjunction or interjection

* 1844 , E. A. Andrews: First Lessions in Latin; or Introduction to Andrews and Stoddard's Latin Grammar. (6th edition, Boston), p.91 ( at books.google)

322. The parts of speech which are neither declined nor conjugated, are called by the general name of particles . 323. They are adverbs, prepositions, conjunctions, and interjections.

* 1894 (2008), B. L. Gildersleeve & G. Lodge: Gildersleeve's Latin Grammar (reprint of the 3rd edition by Dover, 2008), p.9. ( at books.google)

The Parts of Speech are the Noun (Substantive and Adjective), the Pronoun, the Verb, and the Particles (Adverb, Preposition, and Conjunction)[.]

(linguistics, sensu stricto) A word that has a particular grammatical function but does not obviously belong to any particular part of speech, such as the word to in English infinitives or O as the vocative particle.

* {{quote-web

, date = 1965-06-04 , author = Shigeyuki Kuroda , title = Generative grammatical studies in the Japanese language , site = DSpace@MIT , url = http://hdl.handle.net/1721.1/13006 , accessdate = 2014-02-24 , page = 38 }}

In English there is no grammatical device to differentiate predicational judgments from nonpredicational descriptions. This distinction does cast a shadow on the grammatical sphere to some extent, but recognition of it must generally be made in semantic terms. It is maintained here that in Japanese, on the other hand, the distinction is grammatically realized through the use of the two particles wa and ga.

*

Traditional grammar typically recog-
nises a number of further categories: for example, in his Reference Book of
Terms in Traditional Grammar for Language Students'', Simpson (1982) posits
two additional word-level categories which he refers to as ''Particle'', and
''Conjunction''. Particles include the italicised words in (58) below:
(58) (a)      He put his hat ''on''
       (b)      If you pull too hard, the handle will come ''off''
       (c)      He was leaning too far over the side, and fell ''out''
       (d)      He went ''up to see the manager

(physics) Any of various physical objects making up the constituent parts of an atom; an elementary particle or subatomic particle.

* 2011 , & Jeff Forshaw, The Quantum Universe , Allen Lane 2011, p. 55:

What, he asked himself, does quantum theory have to say about the familiar properties of particles such as position?

*{{quote-magazine, year=2012, month=March-April

, author=(Jeremy Bernstein) , title=A Palette of Particles , volume=100, issue=2, page=146 , magazine=(American Scientist) citation , passage=The physics of elementary particles' in the 20th century was distinguished by the observation of ' particles whose existence had been predicted by theorists sometimes decades earlier.}}