from The American Heritage® Dictionary of the English Language, 5th Edition.

  • noun A part or particle considered to be an irreducible constituent of a specified system.
  • noun The irreducible, indestructible material unit postulated by ancient atomism.
  • noun An extremely small part, quantity, or amount.
  • noun The smallest unit of an element, having all the characteristics of that element and consisting of a very small and dense central nucleus containing protons and neutrons, surrounded by one or more shells of orbiting electrons. Atoms remain undivided in chemical reactions except for the donation, acceptance, or exchange of valence electrons.
  • noun This unit regarded as a source of nuclear energy.

from The Century Dictionary.

  • To reduce to atoms; atomize.
  • noun An extremely minute particle of matter: a term used generally with certain philosophic or scientific limitations.
  • noun A particle of matter assumed not to be divided under the circumstances considered; a molecule.
  • noun In chem. and physics, the unit of matter; the smallest mass of an element that exists in any molecule. The number of kinds of atoms is the same as the number of the elements. All atoms of the same element have the same constant weight. They are for the most part combined with other atoms, either of the same or of a different kind, forming molecules, and are indivisible by chemical force. The atom is sometimes called the chemical unit, in distinction from the molecule or physical unit, the latter being the smallest particle of any kind of matter which can exhibit all the properties of that matter; but atom is also sometimes used as synonymous with molecule in this sense.
  • noun Hence Anything extremely small; a minute quantity: as, he has not an atom of sense.
  • noun The smallest division of time, equal to about ⅙ of a second.
  • noun Anything indivisible; an individual.

from the GNU version of the Collaborative International Dictionary of English.

  • noun An ultimate indivisible particle of matter.
  • noun An ultimate particle of matter not necessarily indivisible; a molecule.
  • noun A constituent particle of matter, or a molecule supposed to be made up of subordinate particles.
  • noun (Chem.) The smallest particle of matter that can enter into combination; one of the elementary constituents of a molecule.
  • noun Anything extremely small; a particle; a whit.
  • transitive verb obsolete To reduce to atoms.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

  • noun The smallest, indivisible constituent part or unit of something.
  • noun 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.
  • noun mathematics A non-zero member of a Boolean algebra that is not a union of any other elements.
  • noun historical A theoretical particle of matter, imagined to be incapable of further division; the smallest possible unit of substance.
  • noun obsolete The smallest medieval unit of time, equal to fifteen ninety-fourths of a second.
  • noun computing, programming An individual number or symbol, as opposed to a list. A scalar value.
  • noun A very small amount.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • noun (physics and chemistry) the smallest component of an element having the chemical properties of the element
  • noun (nontechnical usage) a tiny piece of anything


from The American Heritage® Dictionary of the English Language, 4th Edition

[Middle English attome, from Latin atomus, from Greek atomos, indivisible, atom : a-, not; see a– + tomos, cutting (from temnein, to cut; see tem- in Indo-European roots).]

from Wiktionary, Creative Commons Attribution/Share-Alike License

From Old French atome, from Latin atomus ("smallest particle"), from Ancient Greek ἄτομος (atomos, "indivisible"), from ἀ- (a-, "not") + τέμνω (temnō, "I cut").


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  • By the time I was 5 years old, my oldest brother had a degree in physics. My mother liked to make the joke that "I was taught in school that you could not split an atom; now my son does it." Hence, I always envisioned atoms to be something you could put on a chopping block and split with an axe.

    July 10, 2007

  • Incidentally, I who know very little about this stuff have always wondered if that could be theoretically possible -- if your axe was sharp enough and if you could hit the atom precisely. I don't suppose it is, but just IMAGINE what could happen if an innocent lumberjack inadvertently wielded the power of nuclear holocaust. ;-)

    July 10, 2007

  • That would have to be one incredibly sharp axe, with an edge you wouldn't even be able to see. Funny, I always thought about that too.

    And you'd really, really want to be nice to the lumberjack.

    July 10, 2007

  • Well, it would seem that even a dull axe would at some point have a "leading" atom that would make it atom v. atom. Didn't Zeno of Elea say something about lumberjacks? Can't remember...

    July 10, 2007

  • Indeed, you would not want to get crosswise with the man with the axe. And out west, that would mean calling him a logger rather than a lumberjack. It is a regional thing. They get testy about that.

    July 10, 2007

  • Oh, but lumberjack sounds so pronky.

    July 10, 2007

  • I think that might be the problem!

    WMDs pronk.

    July 10, 2007

  • Yes, I have always liked the word lumberjack, but they are a breed apart from loggers. You have to trust me on this one. ;-)

    July 10, 2007

  • Scary thought--those pronky WMDs. Let's hope they are phantoms.;-)

    July 10, 2007

  • Thanks for the warning, slumry. Next time I go west, I'll remember that. Never cross a person wielding an axe....

    Wait--I don't suppose they still use those, do they?

    July 10, 2007

  • They still use axes to chop wood, of course. As for logging, I would assume there is still a minor role for the axe.

    However, since *most* of the trees have been cut down, there is less need for logging equipment of any sort. It is a touchy subject in these parts. And don't say "spotted owl" to a logger unless you are prepared for unpleasantness!

    July 10, 2007

  • I would never. Even though I like spotted owls. :-)

    July 10, 2007

  • The idea of the atom as an indivisible smallest piece you can cut something into goes back to Epicurus (341—271 BCE)

    September 28, 2013