The double dactyl is a verse form invented by Anthony Hecht and Paul Pascal in 1951.
Some purists still follow Hecht and Pascal's original rule that no single six-syllable word, once used in a double dactyl, should ever be knowingly used again.
[1] An example by John Hollander:[1] Higgledy piggledy, Benjamin Harrison, Twenty-third president Was, and, as such,
P.[2] A McWhirtle is a light verse form similar to a double dactyl, invented in 1989 by American poet Bruce Newling.
McWhirtles share essentially the same form as double dactyls, but without the strict requirements, making them easier to write.