It is well known that hexagons can be used to tile a flat surface with no space left over. If letters are inscribed in the hexagons, a three-letter word can be formed by a set of three hexagons meeting at a common point. No rearrangement of letters is necessary; the word can always be spelled out by going either clockwise or counterclockwise around the point. Because this property does not hold for square tiling (four-letter words) or triangular tiling (six-letter words), hexagonal tiling is uniquely suited for the various letter patterns we described in this article.
Eckler, A. Ross
Word Ways: Vol. 13
, Article 17.
Available at: http://digitalcommons.butler.edu/wordways/vol13/iss2/17