I have often wondered about the longest word in the English language that uses any letter only once. For example, the word "facetiously" is 11 letters long and meets the criteria (it also happens, as many people know, to be one of the few words to use all the vowels IN ORDER). But I imagine there must be other long words that only use letters once. Any thoughts or remembrances?

abstemiously has twelve(12) letters with all the vowels in order (I think). [and it is heterological!]

The longest English isogram I know is 'pneumoventriculography.'

he longest English isogram I know is 'pneumoventriculography.'

The e is repeated, as are the n, o, and r. The Wikipedia article (link) goes over some of the well-formed contenders.

Isogram –noun Meteorology, Geography. a line representing equality with respect to a given variable, used to relate points on maps, charts, etc.

Also called isoline.

See how confusing this world can be.

I dug through all the links on onelook and I only found Topher's definition of isogram in one dictionary. The ever reliable Wiktionary@

To all who answered this question, THANK YOU! What wonderful words there are out there...I had never thought of "ambidextrously", which is at 14 letters is awfully good. Uncopyrightables is even better at 16. These are words one might even see in real life, depending on one's profession. "Subdermatoglyphic" is more sublime! But thanks for the Wiki link. I am a happy wordsmith now!