Matanawí
Matanawí was a language isolate once spoken in Brazil.
An isolate: no relationship to any other known language has been demonstrated.
Matanawí (Matanauí, Mitandua, Moutoniway) is an extinct divergent Amazonian language isolate that may be distantly related to the Muran languages. It was originally spoken on the Castanha River and Madeirinha River in Amazonas State.
From Wikipedia · Matanawí language · CC BY-SA 4.0