hapax legomenon
/ˈhæpæksləˈgɒmɪnɒn/noun
(pl. hapax legomena /-mɪnə/)
- a term of which only one instance of use is recorded（在过去）仅出现过一次的词（或短语）。
词源
mid 17th cent.: Greek， 'a thing said once'， from hapax 'once' and the passive participle of legein 'to say'.