The Arapaho language or Arapaho proper (also spelled "Arapahoe"; in Arapaho: Hinóno’eitíít ) is a one of the Plains Algonquian languages, closely related to Gros Ventre and other Arapahoan languages. It is spoken by under 300 people over age 50 in Wyoming, and in Oklahoma by "only a handful of people . . . all near eighty or older". As such, it is in danger of becoming extinct. As of 1996, there were approximately 1,000 speakers among the Northern Arapaho. As of 2008, the authors of a newly published grammar estimated there were slightly over 250 fluent speakers, plus "quite a few near-fluent passive understanders". In 2008, it was reported that a school had been opened to teach the language to children.

Among the sound changes in the evolution from Proto-Algonquian to Arapaho are the loss of Proto-Algonquian *k, followed by *p becoming either /k/ or /tʃ/; the two Proto-Algonquian semivowels merging to either /n/ or /j/; and *m often becoming /b/. Arapaho is unusual among Algonquian languages in retaining the contrast between the reconstructed phonemes *r and *θ (generally as /n/ and /θ/, respectively). These and other changes serve to give Arapaho a phonological system very divergent from that of Proto-Algonquian and other Algonquian languages, and even from languages spoken in the adjacent Great Basin. Some examples comparing Arapaho words with their cognates in Proto-Algonquian can illustrate this:

The Plains Indians are the Indigenous peoples who live on the plains and rolling hills of the Great Plains of North America. Their equestrian culture and resistance to domination by Canada and the United States have made the Plains Indians an archetype in literature and art for American Indians everywhere. Plains Indians are usually divided into two broad classifications which overlap to some degree. The first group were fully nomadic during the 16th to 19th centuries, following the vast herds of buffalo, although some tribes occasionally engaged in agriculture; growing tobacco and corn primarily. These include the Blackfoot, Arapaho, Assiniboine, Cheyenne, Comanche, Crow, Gros Ventre, Kiowa, Lakota, Lipan, Plains Apache (or Kiowa Apache), Plains Cree, Plains Ojibwe, Sarsi, Nakoda (Stoney), and Tonkawa.

The second group of Plains Indians includes the aboriginal peoples of the Great Plains, as well as the Prairie Indians who come from as far east the Mississippi River. These tribes were semi-sedentary, and, in addition to hunting buffalo, they lived in villages, raised crops, and actively traded with other tribes. These include the Arikara, Hidatsa, Iowa, Kaw (or Kansa), Kitsai, Mandan, Missouria, Omaha, Osage, Otoe, Pawnee, Ponca, Quapaw, Santee, Wichita, and Yankton Dakota.