I've been looking for the antonym of dense. I'm looking for an exact opposite: a single word the means, precisely, "having less mass per unit volume than another object".

That is, I'm seeking a scientific word which could be put into this sentence, and have it make sense:

Wood is more _____ than metal

To mean precisely the opposite of:

Metal is denser than wood

And precisely the same as:

Wood is less dense than metal

Only using a single word (as an atomic comparative), as opposed to the two words "less dense".

As analogies, we have the pairs "heavy"/"light" and "thin"/"thick", and thus needn't to resort to circumlocutions like "more massive" or "less wide".

For similar reasons, I find "light" (the opposite of "heavy") and "spread out" (the opposite of "congested", i.e. "smaller population per unit volume") unsatisfying. I would like a single, atomic word that enjoys some currency in scientific prose, which means precisely "less mass per unit volume".

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    Wood is less dense than metal -- Less Dense IS a science word. – John Lawler Aug 8 '14 at 18:48
  • How do you define a "science word"? – Matt Gutting Aug 8 '14 at 18:57
  • @Matt Gutting A quote. – Edwin Ashworth Aug 8 '14 at 21:35

In statistical physics, density is an important concept, and I have not encountered it used in any way to suggest it has an antonym, sorry to say.

So, I would have to conclude that there is no "science word" for less dense in a general sense. Rarified only applies to gases, and often only to air pressure when discussing the propagation of sound waves.

The intensive property is density and when a given material has a larger or smaller value for density than some other material, we just use "more" or "less" as appropriate descriptors.

Depending on your context, you could possibly use the word diffuse, which has the general meaning of things that are more spread apart, but I would not consider it an exact antonym to the scientific usage of dense.

  • Per meta.english.stackexchange.com/a/364 for the use–mention distinction, please use an italic face not a bold one. It makes the page look too heavy otherwise, and furthermore runs counter to typographic convention both on this site and in scholarly works. Per meta.english.stackexchange.com/a/364 for the use–mention distinction, please use an italic face not a bold one. It makes the page look too heavy otherwise, and also runs counter to typographic convention both on this site and in scholarly works. Please do’t use capitalized words for the use–mention distinction, either. – tchrist Aug 13 '14 at 15:58

Density is a property of all matter. It is the mass per unit volume. SeeWikipedia

If you are comparing two materials, one will be more dense or less dense than the other.

This is more appropriate than trying for an antonym-pair (like heavy/light)


Try sparser or scanter........

  • Sparse is a mathematical term used in opposition to dense. Good one. – Matt Gutting Aug 8 '14 at 18:57
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    But dense in mathematics doesn't mean the same thing as dense in physics. Physical density is a measurable and variable property of matter -- a mass noun; mathematical density is a property of ordered sets which is either true or false, with no variation. Physically, dense and compact mean the same thing. Mathematically they don't. And sparse doesn't apply to ordered sets; it's only defined for matrices and other constructs. – John Lawler Aug 8 '14 at 19:09
  • Plus “Wood is sparser than metal” has nothing to do with the density at all, but with how easy the materials in question are to obtain. – Janus Bahs Jacquet Aug 27 '14 at 19:12


This is the precise scientific term used to describe something as being not dense/less dense.

  • Do you have a citation for that? Can it be used of a homogenous material, as opposed to the distribution of a material in a different matrix? In other words, would anyone on the planet say "wood is rarer than iron" to mean wood has less mass per unit volume than iron? – Dan Bron Aug 8 '14 at 21:10
  • Yes, relation to density it can be used to describe both things like different gases and different solids. Definition wise it's usually just defined as "Not dense"; see link. Here's an example of it being used to describe a solid - link – Niall Aug 8 '14 at 21:20
  • Collins specifically indicates that the term is applied only to gases: rare: (General Physics) (of a gas, esp the atmosphere at high altitudes) having a low density; thin; rarefied. AHD and RHK Webster's use 'thin' as a synonym here, which is never applied to solids wrt density. Have you a recognised authority (rather than a use in a set of scientific teaching notes) licensing the use of say 'lead is rarer than gold at the same temperature'? – Edwin Ashworth Aug 8 '14 at 21:47

I have given up trying to find a proper scientific term for this property. You can try adding a prefix or suffix to impart the property you want in a way that is clearly understood by audience.

Essentially you want "not dense". Given that "dense" is latin in origin, nondense seems appropriate, but denseless seems to have a better ring to it.

wood is more denseless than metal

The reciprocal of density is sometimes referred to its specific volume, so you could say:

wood has more specific volume than metal

But I didn't find a single term related to specific volume the same way dense relates to density.

  • @ab2: specific volume is related to specific gravity, but I was making a pun between dense and sense. – jxh Dec 9 '16 at 20:17

The opposite of dense is rare, i.e. wood is rarer than metal, metal is denser than wood.

marked by wide separation of component particles : thin (MW)

I believe you could also use subtile, usually used as not dense, rarefied or thin.

  • 1
    An interesting suggestion, but rare has an obvious common usage that is entirely different than the desired meaning and would cause readers to constantly have to remind themselves of the intended, extremely secondary meaning, assuming that it had been explicitly spelled out before (especially since wood is clearly more common than metal in the normal sense of the word)... so I don't think it's a good fit. – Hellion Dec 7 '16 at 20:03
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    Welcome to EL&U. I've added a dictionary definition to salvage your answer, as this meaning of rare is nowadays specialized, and in general usage, it is, well, somewhat rare. I encourage you to take the site tour and review the help center for additional guidance. – choster Dec 7 '16 at 20:57

specific gravity

It's not a single word -- I very much doubt you will find a single word -- but it is more scientific-sounding than density.

In your example:

Wood has a lower specific gravity than metal.

From Engineering Toolbox, Specific Gravity (Relative Density)

Specific Gravity - SG - is a dimensionless unit defined as the ratio of the density of a substance to the density of water - at a specified temperature


In everyday usage, one might say " Wood is lighter than metal " and be understood in most contexts.


Adding to the list of efforts:

(The components of) wood has(/have) a higher molar volume than metal.

Density in chemistry/physics is a quantity (usually mass) per unit volume: N/V; Molar volume is its inverse (usually applied to gases): V/N.

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