| Definition -
A word that has either no repeating letters (e.g. ambidextrously) or in which all the letters appear twice (e.g. deed).
1. Isograms in which each letter appears just once are called first-order isograms. Those where each letter appears twice are called either second-order isograms or pair isograms.
Etymology - The term was coined by Dmitri Borgmann in his book Language on Vacation: An Olio of Orthographical Oddities (Scribner, 1965)