hapax legomenon

 
Pronunciation: /ˌhapaks lɪˈgɒmɪnɒn/

noun (plural hapax legomena /-mɪnə/)

  • a term of which only one instance of use is recorded.

Origin:

mid 17th century: Greek, 'a thing said once', from hapax 'once' and the passive participle of legein 'to say'