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A pair isogram (or second-order isogram) is a word in which every distinct letter appears exactly twice throughout the entire spelling (e.g. "intestines" contains 2 i, 2 n, 2 t, 2 e, 2 s).
First classified by recreational linguist Dmitri Borgmann, second-order isograms represent an exceptionally rigid combinatorial constraint. Unlike first-order isograms (where letters never repeat), pair isograms require that every letter without exception appears in duplicate. Famous 10-letter pair isograms include "intestines" (i-n-t-e-s each doubled), "reappear" (r-e-a-p each doubled), "hotshots" (h-o-t-s each doubled), and reduplicative culinary words like "couscous" (c-o-u-s).
Test any word to verify if every letter occurs exactly twice:
Verified English words exemplifying pair isograms (second-order doublet words) with Scrabble scores
Linguistic definitions, etymological origins, and tournament usage
A pair isogram (or second-order isogram) is a word where every unique letter occurs exactly twice, such as "couscous" (2 c, 2 o, 2 u, 2 s) or "intestines" (2 i, 2 n, 2 t, 2 e, 2 s).