Heterogram (linguistics)

A heterogram is a word, phrase, or sentence in which no letter of the alphabet occurs more than once. The defining characteristic is the uniqueness of each letter. Heterograms are a subset of isograms, which only require that each letter appears the same number of times. Therefore, all heterograms are isograms (specifically, isograms where each letter occurs exactly once), but not all isograms are heterograms. The pursuit of constructing long heterograms is a form of recreational linguistics. Constructing heterogrammatic sentences can be a significant challenge.