Huilliche (which can also be found spelt Williche, Huiliche or Veliche) is a moribund branch of the Araucanian language family.

[4] Huilliche is closely related to Mapudungun, the language of the Mapuche, though more research is needed to determine the degree of mutual intelligibility between the two.

The "Enduring Voices" project of National Geographic reports the following:"They are to some degree hidden within the broader Mapuche ethnic group, yet consider themselves quite distinct in both language and identity [...] Though the two languages [Huillichesungun and Tsesungun] may share as many as 80% of basic words, we confirmed that they differ in their sounds and grammar, as well as in their ethno-linguistic identity [...] Unexpectedly, Tsesungun, though it is geographically closer to Mapudungun, is less similar to it.

"The Jesuit priest Luis de Valdivia reported in 1606 that there was linguistic unity in the territory between Coquimbo and Chiloé, from the Pacific to the Andes, and that this was composed of varieties whose differences were mostly in pronunciation and vocabulary.

The latter two noted that Huilliche was the most divergent of the varieties of Araucanian, as did Pilar Álvarez-Santullano, a researcher in the phonology and syntax of Chesungun on the Osorno coast.