Tuesday, 11 October 2022

#18 Parallelepiped ... from old Math Terms notes

 Parallelepiped:  This word for a solid made by intersecting pairs of parallel planes forming six faces that are each parallelograms is rapidly becoming obsolete, although no good word has emerged to replace it. A rectangular or orthogonal parallelepiped is the shape of a room or a shoe box. The word is condensed from the Greek word parallelepipedon for the same shape. The roots are para (beside) + allel (other) + epi (on) and pedon (ground). Parallelepipedon was the word used by Billingsley in his 1570 translation of Euclid, the first known use of the word in English. According to John Conway, this was the common term in use until around 1870 to 1900 when it gave way to parallelepiped; although the OED lists its use by John Playfair as early as 1812. A posting from John Albree of Auburn University cited an earlier use. [In Charles Hutton's *Dictionary* (volume 2, 1795, p.199), the terms "parallelopiped" and "parallelopipedon" are presented equally, and he remarks that such a polyhedron "is only a particular species" of a prism.]

This newer term now seems headed for demise due to changes in school curriculum and the reduced coverage of solid geometry, although one correspondent suggests that "parallelepipedo" would be known by most Spanish students. I was somewhat surprised to find that parallelepiped is present in my computer spell check, which I find often omits technical terms.

The word is pronounced with the accent on the epi syllable. The para root is common in math words and is related to other words like parlor, paragraph, and parable. Allel became our alter, for other, and gives us alternate and alternative. The epi root shows up in epidermis (on the skin), epitaph (over the grave), epicycle (on the circle), and epidemic (on the people). Pedon is from ped for foot, and was also generalized for plane.

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