• (RP) IPA: /ˈatəm/
• (GA) enPR: ăt'əm, IPA: /ˈætəm/, [ˈæɾəm]

atom (plural atoms)

1. (chemistry, physics) 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. [from 16th c.]
2. (history of science) A hypothetical particle posited by Greek philosophers as an ultimate and indivisible component of matter. [from 15th c.]
3. (now generally regarded figuratively) The smallest, indivisible constituent part or unit of something. [from 17th c.]
4. (philosophy) In logical atomism, a fundamental fact that cannot be further broken down.
5. (historical) The smallest medieval unit of time, equal to fifteen ninety-fourths of a second. [from 10th c.]
6. A mote of dust in a sunbeam. [from 16th c.]
7. A very small amount; a whit. [from 17th c.]
   • 1945 August 17, George Orwell [pseudonym; Eric Arthur Blair], chapter 1, in Animal Farm: A Fairy Story, London: Secker & Warburg, OCLC 3655473 ↗:

     Now, comrades, what is the nature of this life of ours? Let us face it, our lives are miserable, laborious, and short. 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. No animal in England knows the meaning of happiness or leisure after he is a year old. No animal in England is free. The life of an animal is misery and slavery: that is the plain truth.

8. (computing, programming, Lisp) An individual number or symbol, as opposed to a list; a scalar value. [from 20th c.]
9. (mathematics, algebra) A non-zero member of a Boolean algebra that is not a union of any other elements. Or, a non-zero member of a Boolean lattice that has only zero below it. [from 20th c.]

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

10. (mathematics, set theory) An element of a set that is not itself a set; an urelement. [from 20th c.]
11. (usually capitalised as "Atom") A member of an age group division in hockey for ten- to 11-year-olds.

• See also Thesaurus:atom
• (small amount) see also Thesaurus:modicum.

• French: atome
• German: Atom
• Italian: atomo
• Portuguese: átomo
• Russian: а́том
• Spanish: átomo

• French: atome
• German: Atom
• Italian: atomo
• Portuguese: átomo
• Russian: а́том
• Spanish: átomo

• Italian: atomo
• Portuguese: átomo