language isolate
A natural language with no demonstrable genealogical relationship to other languages. Used in linguistics.
Basque is considered the only language isolate in Europe.
There is debate over whether Japanese is a language isolate.
孤立語 (isolating language) refers to a language with little or no morphology, where each word tends to be a single morpheme. 孤立した言語 (language isolate) refers to a language with no known relatives.
Compound of 孤立 (isolated) + した (past attributive form of する) + 言語 (language). The term is a direct translation of the English 'language isolate'.