hapax legomenon

Rank-frequency plot for words in the novel Moby-Dick. About 44% of the distinct set of words in this novel, such as "matrimonial", occur only once, and so are hapax legomena (red). About 17%, such as "dexterity", appear twice (so-called dis legomena, in blue). Zipf's law predicts that the words in this plot should approximate a straight line with slope −1.

In corpus linguistics, a hapax legomenon (/ˈhæpəks lɪˈɡɒmɪnɒn/ also /ˈhæpæks/ or /ˈheɪpæks/; pl. hapax legomena; sometimes abbreviated to hapax, plural hapaxes) is a word or an expression 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 also sometimes used to describe a word that occurs in just one of an author's works but more than once in that particular work. Hapax legomenon is a transliteration of Greek ἅπαξ λεγόμενον, meaning "said once".