Hapax legomenon
A
hapax legomenon is a word that occurs only once within a context, either in the written record of an entire language, in the works of an author, or in a single text. The term is sometimes incorrectly used to describe a word that occurs in just one of an author's works, even though it occurs more than once in that work.
Hapax legomenon is a transliteration of Greek ἅπαξ λεγόμενον, meaning " said once". The related terms
dis legomenon,
tris legomenon, and
tetrakis legomenon respectively refer to double, triple, or quadruple occurrences, but are far less commonly used.
Hapax legomena are quite common, as predicted by Zipf's law, which states that the frequency of any word in a work is inversely related to its rank in the frequency table. For large corpora, about 40% to 60% of the words are
hapax legomena, and another 10% to 15% are
dis legomena. Thus, in the Brown Corpus of American English, about half of the 50,000 words are
hapax legomena within that corpus.