On page 844 of volume 16 of the 1888 edition of the Encyclopedia Britannica, you will learn that ctenophores furnish examples of eight-sided amphithect pyramids. On reading this, you will of course think “Amphithect?”
You might from there go to a dictionary. If you do, hard luck for you: it’s not even in the Oxford English Dictionary. You might try to guess the meaning; the amphi will lead you to imagine it has to do with double-sidedness or something similar. But what about the thect? What the heck is that? Does it relate to tect as in architect? Nope. And good luck finding it in your handy little Pocket Oxford Classical Greek Dictionary.
You may find yourself down for the count or at least out of the court (the ct), just saying the word again and again, bouncing as it does across the various enunciatory positions – two lips /m/, lips and teeth /f/, tongue and teeth /θ/, back of tongue /k/, and finally tip of tongue on alveolar ridge /t/. Say it repeatedly and you make a neat circuit of your mouth. Pluralize it – amphithects – to get an extra fricative just to lubricate it further.
You can also play with the letters. Amp, hit, he; am, phi, the… match the pi, ham pith etc., at the chimp, hm – pathetic…
And while you’re doing that, perhaps your eyes will coast up the page a bit (page 844, remember? column 1) and see this:
In the highest and most complicated group, the Heterostaura, the basal polygon is no longer regular but amphithect (αμιθηκτος = double-edged). Such a polygon has an even number of sides, and can be divided into symmetrical halves by each of two places intersecting at right angles in the middle point, and thus dividing the whole figure into four congruent polygons.
An amphithect pyramid is thus one that has, for instance, a rhombus as its base. Which you would have learned earlier if you hadn’t gotten on the wrong bus, so to speak. But no wonder it was all Greek…
What? Ctenophores? Oh, yes, I’ll get to those next.