By analogy with anthropomorphisms given in Webster's Third Edition, the plural form anti-anthropomorphisms can be inferred. Having eliminated these three groups of words, we can now begin the search for true isograms. Starting with pair isograms, in which each letter appears twice, we find numerous eight-letter examples. The Caucasus is a mountain range between the Black and Caspian Seas given in Webster's New Geographical Dictionary, and Vivienne is a common feminine given name. Slake kales and tessellata are both taken from Webster's Third Edition.
Longer specimens are very elusive.
Note that Taeniodontidae is a pair isogram of the horseshoer variety, with letters in the first half repeated in the second. The only known pair isogram of more than fourteen letters is the French word antiperspirantes . Surely there must be legitimate pair isograms of more than fourteen letters in some English reference work. Next we progress to trio isograms, in which each letter used in the word occurs three times. In this way it is possible to get an acceptable, albeit apostrophized, fifteen-letter trio isogram.