isogram, noun – a word in which the letters turn up an equal number of times.

There are different types of isograms depending on how many times each letter appears:

In a first-order isogram, each letter appears just once, as in dialogue, lexicography, ambidextrously and uncopyrightable.

In a second-order isogram, each letter appears twice, as in deed, Vivienne, Caucasus and intestines.

In a third-order isogram, each letter appears three times. These are rare, unusual words such as deeded (“conveyed by deed”) and geggee (“victim of a hoax”).

I came across this term in an article by David Crystal about his new book By Hook or By Crook: A Journey in Search of English.