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.}}