What is the meaning of aclastic? Does it really have any use in an optical sense? The major on-line dictionaries don't include it. (I haven't access to the OED.)

Dorland's Illustrated Medical Dictionary says:

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aclastic (aclas·tic) (a-klas¢tik) 1. pertaining to or characterized by aclasis. 2. not refracting.

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and

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aclasis (acla·sis) (ak¢l[schwa]-sis) [a-1 + Gr. klasis a breaking] pathologic continuity of structure, as in multiple exostoses.

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Two other on-line word collections (Luciferous Logolepsy and Hutchinson's Dictionary of Difficult Words) include a very brief definition:

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aclastic
adj. - non-refractive.

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These look like they could be lifted from Dorland.

If it does mean non-refractive in an optical sense then it's easy to see why the word wouldn't have much use. You can't say that a material is non-refractive without specifying the medium in which it is non-refractive, e.g., a crystal whose refractive index was identical to that of water would be aclastic in water. The number of interfaces between different materials that could be described as exactly aclastic is zero. It seems like a word that has nothing useful to add to any discussion of optics.

Given the medical meaning of the word, I wonder if the definition started as "aclastic: non-refractory," using refractory in one of its medical senses: unresponsive to treatment or resistant to infection.

Virge, excellent question. I haven't responded partly because I have had annoying computer problems, and partly because I don't know. My Taber's Medical Dictionary doesn't mention "non-refractive." It defines aclasis, aclasia as: "[Gr. a-, not, + klasis, a breaking away] Abnormal tissue arising from and continuous with a normal structure, as in chondrodysplasia. disphyseal a. Imperfect formation of cancellous bone in cartilege between diaphysis and epiphysis."

I will ask my logophile friend, though. He is a physician, knows more about words than anyone I know, and has a special knowledge in optical medicine. I will get back to you on that. In the meantime, does anyone else here know? I am surprised that Dorland's Medical Dictionary mentions "non-refractive" and Taber's doesn't.

My logophile friend wrote me this:

"'aclastic' to me suggests 'unbreakable'.
I will search and tell you what I find."

If he doesn't find anything, I will go to a medical library.

I thought my colleague would have something to add here, but he didn't. He found the same online definitions that you did. However, he did find a site with a glossary that showed that 'clastic' is a geologic term for shattered rock. That doesn't really help, though.

I went to OEDILF and found the limerick in question. I suppose it works as is, though I might suggest using the medical definition of the word. Here is an example:

Aclasis is tissue aberrant
That grows from a regular parent.
Your cart'lege may show
Some bone, even though
It shouldn't -- and that's quite apparent.

Just a suggestion.

This message has been edited. Last edited by: Kalleh,

On second thought...your definition, along with the author's note, may be better. I went to the library's OED (2nd. Ed), and it doesn't have the medical definition. Here is what it says:

aclastic (e' klaestik) [I don't have those funny pronunciation fonts that jheem has; the "e" was upside down, and the "ae" were connected.], a. Nat. Phil. rare. [f. Gr. unbroken + -ic] Not refracting; applied to substances which do not refract the rays of light which pass through them. 1879 Syd. Soc. Lex.

I don't have those funny pronunciation fonts that jheem has

I think you do, K. Run Start Menu > Programs > Accessories > System Tools > Character Map ... or if you cannot find that in the Start Menu, try Star Menu > Run and type charmap and press return. You'll see a map of all your available characters and can click on them and copy and paste into your post. I choose Lucida Sans Unicode for the font I search. Hope this helps.

Well, surprise, surprise! You're right, except I didn't see the upside down "e." Thanks, jheem, it does help! [Now I have to remember how to get there again. ]

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Originally posted by Kalleh:
On second thought...your definition, along with the author's note, may be better. I went to the library's OED (2nd. Ed), and it doesn't have the medical definition. Here is what it says:

_aclastic_ (e' klaestik) [I don't have those funny pronunciation fonts that jheem has; the "e" was upside down, and the "ae" were connected.], _a. Nat. Phil._ rare. [f. Gr. unbroken + -ic] Not refracting; applied to substances which do not refract the rays of light which pass through them. 1879 Syd. Soc. Lex.

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Thanks Kalleh.
I guess the researchers at OUP found enough usage of the word in its optical context to make it worth including. It's a pity they didn't see fit to include an example of an aclastic substance. I suppose, if you take your measurements in normal room conditions, you should be able to find a substance (a gas) that can be kept at a pressure such that at one particular wavelength the substance is aclastic (wrt air).