A hapax legomenon (often abbreviated just to hapax) is a word which appears only once -- in a language, a single written work, or the entire body of work of a given author. According to Wikipedia: "Hapax legomenon is a transliteration of Greek ???? ?????????, meaning '(something) said (only) once.'"
Hapaxes are everywhere, particularly in historical texts -- indeed, many of the remaining untranslated hieroglyphs appear to be hapaxes, possibly because we lack enough text to see them more frequently --... READ ON