> I'm asking this question for William Blackwell, who has yet to get > connected but hopes to do so soon: > > A finite straight line has two sides and can be considered a regular > n-gon where n = 2. (This line is also a rectangle with length, but 0 > width, an ellipse with one axis = 0, an isosceles triangle with base > = 0, and so on. In every case it has two sides.) Is there a correct > "gon" > term (besides" line segment") for this shape? A bigon? duogon? digon? > > Thanks in advance for your help. William has lots of reasons to be > interested > in this shape which he looks forward to sharing when he gets online. > The only term of these three that is properly formed is "digon", and in fact this term has often been used with this meaning.
"di" is Greek, and so is the natural prefix to mate with the Greek-derived "gon", meaning "angle".
"bi" (abbreviating "bis") is the Latin equivalent - it mates for example with Latin-derived "lateral" to give "bilateral", meaning "two-sided", which you might also use in this sort of context. [I have sometimes seen the form "bigon", but regard it as incorrect.]
"duo" is a Latin combining form, used in making words like "duodecimal" (= "12-ary").
The word "dihedron" is fairly well-accepted for the similar degenerate polyhedron with just two faces, especially in its adjectival form "dihedral".