I am looking for an antonym for dense in the context of material properties. Specifically, bulk materials which possess negligible porosity, i.e. sound materials.

An example usage sentence might be

Steel is more dense than aluminum, but aluminum is more [_] than steel.

Naturally, one should simply say "less dense" instead of "more [_]" as the former is idiomatic and unambiguous. Still, there is a nagging curiosity of whether such an ideal antonym exists.

Colleagues and I have thought of several candidate words which do not quite have the right meaning, but might be close:

  • airy: implies porosity and/or the presence of air
  • light: not the correct semantics as this word applies to weight
  • sparse: seems to imply atoms are further apart, which is generally not correct (density has little or no correlation with interatomic spacing in homogeneous mono-atomic materials)

and for fun, a made-up word which immediately springs to mind: un-dense.

Are there any superior antonym choices for the desired meaning?

  • I think you'll have to go with '*less dense than'.
    – user66974
    Commented Nov 10, 2015 at 7:20
  • @Josh61 I believe you're almost certainly correct, and in materials science it is what I most commonly see used (hence idiomatic), but it's always worth a shot. Commented Nov 10, 2015 at 7:29
  • I also found myself considering "un-dense"
    – goodguy5
    Commented Jun 28, 2021 at 17:54

3 Answers 3


The actual word that's in use today is "light," believe it or not. "Rare" has a whole bunch of connotations you don't need, and "rarefied" means altogether something else. So, yeah, light metal and, believe it or not, heavy metal.

Or, if you wish to sound science-y and all, high-density and low-density. Believe it or not.

To summarize:

Aluminum is a lighter metal than steel. (Or aliminium, should you wish to please the British contingent).

Once again, my apologies.

  • 1
    Yes, you are right. Density is merely an expression of weight to volume. Aluminium is lighter than steel. There seems to be no opposite to dense - so far as physics is concerned. However if you are talking about something like density of population, you could use sparsity.
    – WS2
    Commented Nov 10, 2015 at 7:45
  • @WS2: Unless you consider "flimsy" and "ethereal."
    – Ricky
    Commented Nov 10, 2015 at 7:49
  • I don't believe flimsy is an antonym of dense. And ethereal is usually used in a metaphysical sense. One wouldn't talk about aluminium being more ethereal than steel!
    – WS2
    Commented Nov 10, 2015 at 8:23
  • @WS2: Good. Cookie?
    – Ricky
    Commented Nov 10, 2015 at 8:36
  • 2
    "Aliminium" doesn't please this British contingent.
    – Rupe
    Commented Nov 10, 2015 at 10:12

I will go with tenuous.

tenuous: not dense : rare M-W

tenuity: the quality or condition of being tenuous; lack of thickness, density, or substance AHD

Like copper, alumiminum is a soft, tenuous metal, remarkable for its freedom from corrosion Books Google

  • Interesting answer, the word's direct meaning makes it seem like a great choice. Humorously, copper is almost three times as dense as aluminum, so I am not so sure about that particular book's word choice in this situation based on the supplied definitions. All the same I do like the word. Commented Nov 10, 2015 at 14:18

The opposite term is 'rare'. 'Dense' in this sense:

  1. Having its constituent particles closely compacted together; thick, compact.
    a. Of close molecular structure. Opp. to rare.

and 'rare' in this sense:

  1. a. Originally: (of an organ or tissue, soil, or other substance) having the constituent material or particles loose or not closely packed together; not dense or compact; attenuated. In later use chiefly: (of air or a gas) having low density, thin (though cf. rare gas n. at Special uses 2). Also fig., with reference to the workings of the mind: refined, subtle, rarefied.

[Emphasis mine. "dense, adj.". OED Online. September 2015. Oxford University Press. http://www.oed.com/view/Entry/50026?rskey=kF0Cmr&result=1&isAdvanced=false (accessed November 10, 2015) and "rare, adj.1 (and int.), adv.1, and n.". OED Online. September 2015. Oxford University Press. http://www.oed.com/view/Entry/158248?rskey=OGVNsI&result=1&isAdvanced=false (accessed November 10, 2015).]

Thus, 'rare' works with the comparative in your example, even though it is susceptible to misinterpretation through ignorance:

Steel is more dense than aluminum, but aluminum is more rare than steel.

It also works without the comparative, although it is again, possibly, among non-specialists, easily misinterpreted:

rare earth, n.
Originally: any of various naturally occurring oxides of elements of the lanthanide series (or †of other metallic elements).

  • I would only use "rare" for gasses, and even then very carefully, and never as a comparative. If you were to say that aluminum is rarer than steel, I would contradict you by saying that aluminum is more abundant than iron in the earth's crust. Commented Nov 10, 2015 at 8:09
  • @200_success, I suspect what you would do is not entirely relevant; but anyway, see the examples I just provided.
    – JEL
    Commented Nov 10, 2015 at 8:11

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