Do “asymmetric” and “dissymmetric” have different meaning?

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?

Solution 1:

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."

Solution 2:

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.

Solution 3:

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.

Solution 4:

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.

Solution 5:

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.