–noun, plural hap·ax le·go·me·na [hap-aks li-gom-uh-nuh, hey-paks]
a word or phrase that appears only once in a manuscript, document, or particular area of literature.
[Origin: 1880–85; < Gk hápax legómenon (thing) once said]
hapax legomenon. Dictionary.com. Dictionary.com Unabridged (v 1.1). Random House, Inc. http://dictionary.reference.com/browse/hapax legomenon (accessed: June 27, 2008).
This is the first and only time this word has appeared in this community; it is itself a hapax legomenon. While there are multiple hapax legomena to be found here, many words have been used more than once.