A lipogram (from Ancient Greek: λειπογράμματος, leipográmmatos, "leaving out a letter") is a kind of constrained writing or word game consisting of writing paragraphs or longer works in which a particular letter or group of letters is avoided—usually a common vowel, and frequently E, the most common letter in the English language. Larousse defines a lipogram as a "literary work in which one compels oneself strictly to exclude one or several letters of the alphabet". Extended Ancient Greek texts avoiding the letter sigma are the earliest examples of lipograms.Writing a lipogram may be a trivial task when avoiding uncommon letters like Z, J, Q, or X, but it is much more challenging to avoid common letters like E, T, or A, as the author must omit many ordinary words. Grammatically meaningful and smooth-flowing lipograms can be difficult to compose. Identifying lipograms can also be problematic, as there is always the possibility that a given piece of writing in any language may be unintentionally lipogrammatic. For example, Poe's poem The Raven contains no Z, but there is no evidence that this was intentional.
A pangrammatic lipogram is a text that uses every letter of the alphabet except one. For example, "The quick brown fox jumped over the lazy dog" omits the letter S, which the usual pangram includes by using the word jumps.
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