I get that usually a- (or un-) and di- prefixes mean different things, e.g. uninterested and disinterested. However, both asymmetric and dissymmetric refer to the lack of symmetry (which the NOAD indicates: “lacking symmetry”). Does that make them freely interchangeable?

Bonus points: why the hell does dissymetry have two s?

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    Nit pick: It's dis-interested, so the prefix is 'dis' which makes dissymetric fully valid. Note that 'di' means two, like in dichroic (having two colors). – Macke Sep 17 '11 at 11:03
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    Wait. Being disinterested doesn't mean I have two sinterests? – GEdgar Aug 2 '13 at 20:45
up vote 4 down vote accepted

You are wrong in the question itself.

I get that usually a- (or un-) and di- prefixes mean different things, e.g. uninterested and *dis*interested.

So where did the s magically come up from? Well, nowhere - it was there from the beginning, you just messed up the prefix. It's not a di prefix, it's a dis prefix.

Which already answers your question why there are two s in dissymmetry. Well, because there's the prefix + the base:

dis + symmetry

The same as:

a + symmetry

From what I've heard people use the words and also read a few books which contained them, I can say they are synonymous, but dissymmetry is less "famous."

Asymmetry and dissymmetry have two different meanings in chemistry. I've seen some dictionaries which list technical definitions along the lines of the one Pieter quotes: "symmetry, but in opposite directions as the two hands". I'm not sure what this definition means, or if it makes sense as a technical definition, but it does sound like a mangled version of the correct definition for the term as chemists use it.

In chemistry, the term 'chiral' (stemming from the greek word for hand) describes the property of not overlapping with one's mirror image. Left and right hands are chiral because they are mirror images of each other, but however you reorient them, you will not be able to make them overlap. Conversely an object such as a chair can be reoriented such that it is indistinguishable from its mirror image, and therefore is achiral. Every asymmetrical object, or an object which lacks any elements of symmetry, is chiral, but not vice-versa. Dissymmetrical objects lack a particular element of symmetry called an 'axis of improper rotation', but they may or may not have other elements of symmetry. Every chiral object is dissymmetrical (asymmetrical objects are dissymetrical by definition), but not vice-versa. A chair happens to be dissymmetrical, but is achiral. A screw is an example of a dissymetrical object which is not asymmetrical (screws have rotational symmetry) and is chiral (right and left handed screws are non-overlapable mirror images).

I'm sorry if I went into too much detail. My goal was to explain the relationship between the various technical terms, which the dictionary definition does not reflect.

This is a complex question, that requires an in depth response beyond time available. However, see:

this article (resonance/August2012/p768-778)

for a start in the right direction, historically and linguistically. (Among other things, Louis Pasteur is quoted and explained.)

In a qualitative nutshell, dissymmetric is not equivalent to asymmetric, since dissymmetric objects may possess some symmetry elements, while asymmetric objects lack all elements.

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    Welcome to ELU. I have taken the liberty of changing the url you provided into a live link. ... You might consider editing your answer to inform readers that this distinction obtains specifically in the field of chemistry. – StoneyB Jan 12 '13 at 23:07

In physics, "dissymmetry" is typically reserved for situations where extant symmetry is broken and thus preserves some shadow or memory of its prior symmetry (e.g., a crooked picture on a wall). "Asymmetry" connotes a condition that never was symmetrical and thus possesses no such shadow or memory.

From the OED:
Dissymmetry: 1 a: The opposite of symmetry; b: symmetry, but in opposite directions as the two hands.

Similarly but more extensively, the definition of Dissymmetrical refers also to crystallographic usages of the word.

The usage references only extend back into the 1880's suggesting that the word enters the English language from chemistry, and thus making the chemical definition definitive in some ways.

In an etymological approach to asymmetry, we must refer to the Greek word ἀσυμμετρία that means disproportion. In other words, asymmetry is a lack of symmetry that implies another element for making a comparison. This is an aseptic meaning. A situation where a heterogeneous element is introduced, breaking the proportionality of the parts, between them and in relation to the whole.

A second meaning, in a pejorative sense, what we call dissymmetry – the prefix dis- expresses negation or completeness or intensification of an unpleasant or unattractive action-, will be applied to those situations where a proportional or symmetrical situation was broken in an anomalous or faulty way (i.e. for political pressures, the threat of secession or self-determination, the confusion between powers –if you have differences in culture, religion, language… you could reach more powers in economy, social services or foreign policy or more representatives in State institutions-).

When a territorial organization is based on dissymmetries we have to speak about the pathology of federations, meaning the failure of them. Spanish centrifugal federalism has traditionally based on dissymmetries.

SEIJAS VILLADANGOS, E. (a) (2013): “Asymmetry as an element of federalism: a theoretical speculation fifty years later - readress the Spanish case”, en LÓPEZ BASAGUREN, A.;

ESCAJEDO SAN EPIFANIO, L. (Eds.), The Ways of federalism in Western Countries and the Horizons of Territorial Autonomy in Spain, Vol. 2, DOI 10.1007/978-3-642-27717-7_44, Berlin, Heidelberg, Springer-Verlag, pp. 679-690. p.681

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    This is an interesting answer. You might be able to improve it with better formatting and with links to your references. – Patrick M Mar 28 '14 at 14:59

Asymmetry is the lack of any symmetry, while "dissymmetry" is the violation of symmetry. The map of Engalnd is asymmetric but a human face is dissymetric. But well... this is the usage in french!

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    I think this is the same as an existing answer here. – Andrew Leach Aug 28 '14 at 13:59
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    Welcome to EL&U. To support an existing answer, please use the arrows to the left of the answer to "upvote" it, rather than posting another answer; this is a Q&A site, not a discussion forum. I encourage you to take the site tour and to review the help center for additional guidance. – choster Aug 28 '14 at 14:01
  • @AndrewLeach, choster, I don't quite agree that this is the same as the other answer. – Araucaria Aug 28 '14 at 18:13

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