heterograms

Heterogram is a term used in recreational linguistics to describe a word, phrase, or sentence in which each letter appears only once. The concept is closely related to the notion of an isogram, but while isograms are often classified by the maximum number of times any letter may repeat, a heterogram imposes a strict prohibition on any repetition, making every constituent character unique.

The term originates from the Greek roots “heteros” (different) and “gramma” (letter). It entered the lexicon of word‑play enthusiasts in the late 19th and early 20th centuries, where it was employed in puzzles, pangrams, and constrained writing. Notable early examples include the English word “hydropneumatic” (15 letters, all distinct) and the phrase “Cwm fjord bank glyphs vext quiz” (a pangrammatic heterogram used to test typewriters).

Heterograms are of interest to typographers, cryptographers, and computer scientists because they illustrate constraints on symbol usage. In computational contexts, generating the longest possible heterogram for a given alphabet is a classic combinatorial optimization problem. Algorithms that produce heterograms can also aid in designing fonts and keyboards that avoid visual ambiguity caused by repeated characters.

Related concepts include pangrams (sentences containing every letter of an alphabet at least once), lipograms (texts that omit a particular letter), and antigrams (phrases formed by rearranging letters to produce opposite meanings). While heterograms are not a formal linguistic category, they remain a popular subject in word games, puzzle magazines, and algorithmic challenges.