Equilateral, Isosceles, Scalene - Word Origins

Date: 12/09/2001 at 14:45:26
From: Julian
Subject: Triangle history

I need to find out about the origins of the scalene, isoceles, and 
equilateral triangles. How they were named? Why were they named 
that?

Date: 12/09/2001 at 15:12:56
From: Doctor Sarah
Subject: Re: Triangle history

Hi Julian - thanks for writing to Dr. Math.

From Steven Schwartzman's _The Words of Mathematics - An Etymological 
Dictionary of Mathematical Terms Used in English_ (Mathematical 
Association of America):

equilateral (adjective): from Latin aequus "even, level" and latus, 
stem later-, "side," both of uncertain origin. Related borrowings from 
Latin are bilateral and multiplateral. In geometry an equilateral 
triangle is one in which all sides are equal in length.

isosceles (adjective): from Greek isos "equal," of unknown prior 
origin, and skelos "leg." The Indo-European root (s)kel- "curved, 
bent" is found in scoliosis and colon, borrowed from Greek. In 
geometry, an isosceles triangle or trapezoid has two equal legs. It 
may seem strange that the root means "bent" even though the sides of a 
triangle and a trapezoid are straight, but each leg is bent relative 
to the adjoining legs.

scalene (adjective): from the Indo-European root skel- "to cut." Greek 
skalenos originally meant "stirred up, hoed up." When a piece of 
ground is stirred up, the surface becomes "uneven," which was a later 
meaning of skalenos. A scalene triangle is uneven in the sense that all 
three sides are of different lengths...

- Doctor Sarah, The Math Forum
  http://mathforum.org/dr.math/