a word or word form which is recorded only once in a text, in the work of a particular author, or in a body of literature
This term is from Hellenistic Greek ἅπαξ λεγόμενον (= hapax legomenon), meaning something that has been said once, composed of ancient Greek ἅπαξ, once, and λεγόμενον, use as a noun of the neuter of λεγόμενος (= legomenos), medio-passive present participle of the verb λέγειν (= legein), to speak (English words such as lexis and lexicon are based on this verb). The plural is hapax legomena, after the Greek plural form.
In the past, this term has been particularly associated with biblical commentary (for example, Armageddon is a hapax legomenon in the Bible, it occurs only in the Book of Revelation, 16:16). The Greek form ἅπαξ λεγόμενον first appeared in an English text in Commentary, or, Exposition Upon The XII. Minor Prophets (1654), by John Trapp (1601-69), Church of England clergyman and writer on theology. The Book of Zechariah, 14:20 is, in the Early Version of the Wycliffe Bible:
In that day, it shal be, on whiche thing the bridil [= bridle] of hors is hooly to the Lord; and caudrons shuln be in the hous of the Lord, as cruetis byfore the auter.
But in the King James Version (1611), this verse is:
In that day shall there be upon the bells of the horses, Holiness Unto The Lord; and the pots in the Lord’s house shall be like the bowls before the altar.
John Trapp wrote:
Verse 20. In that day shall there be upon the bels of the horses] hang’d upon their heades, or about their necks. [...] I confesse the word is by some rendred bridles, by others trappings, frontals, collars. ’Tis ἄπαξ λεγόμενον read only here : and hence this variety of interpretations.
In The Young-students-library containing extracts and abridgments of the most valuable books printed in England, and in the forreign journals, from the year sixty five, to this time : to which is added a new essay upon all sorts of learning (1692), by the Athenian Society, the chapter titled A Discourse concerning the Antiquity and Original of the Points, Vowels and Accents that are placed to the Hebrew Bible contains the earliest known instances of the transliterated forms:
Now that we may know the Mind of God in his Word, we must first know what the words themselves do signifie, and properly and literally mean: This we cannot do in many places, without the help of the Rabbins, or of those who have been taught by them, which is much the same, and that on several Accounts; which renders their Work needful, as Leusden in Philologus Hebraeo-mixtus, pag. 115, &c. and others do manifest: As, 1st. Because many words, as to the Grammar and sense of them, could not be known without the help of those Masters of the Hebrew Tongue; as, Ioel 2.5., Ioel 2.8, &c. 2. There are many words but once used in Scripture, especially in such a sence, and are called the Apax legomena, or ein lo chober bemikr, which we cannot know the meaning of without their help.
The singular form is used instead of the plural in the same chapter:
It is impossible that the whole Pronunciation of the Bible could be preserved so long as a Thousand Years from Ezra, until A. D. 500. under that calamitous state of the Jews, whilst the Tongue ceased to be vulgarly pronounced or known amongst them. The Rabbies themselves (the only supposed Preservers of it) lamenting they had so lost it in this time, that they found great difficulty to explain the Apax Legomenon, or words that are but once used in Scripture; of which there are many.
The shortened form hapax appeared in the late 19th century. In The faith delivered once for all, a sermon preached at Evanston, Illinois, on 10th May 1887, Bishop Cyrus D. Foss of the Methodist Episcopal Church said:
The truth was delivered to, not invented by man, not reasoned out by man’s intellect; delivered, handed by God to man; delivered once for all. That is what hapax means, ‘once for all.’ Read your new version, and you will find it is “once for all delivered.” Delivered in its completeness. The same word is used in another text that will help us to understand this. “It is appointed unto man once to die;” hapax, once, and only once. Such is the divine intent of this word.