mariachi

1. not comparableOf or pertaining to a traditional form of Mexican music, either sung or purely instrumental.
2. not comparableOf or pertaining to a band playing such music, or to the singers of such songs.

plural mariachis

1. A traditional form of Mexican music, either sung or purely instrumental.
2. A group that plays mariachi music.

   At her first performance with an all-male mariachi, the oldest member said to the musical director,[…](No! I've never played with a woman; I'm not going to start now [my translation]).

   2002, Leonor Xóchitl Pérez, “8: Transgressing the Taboo: A Chicana's Voice in the Mariachi World”, in Norma Elia Cantú, Olga Nájera-Ramírez, editors, Chicana Traditions: Continuity and Change, page 151

   1 more example

   2004, "Mariachi," entry in Cordelia Candelaria, Peter J. García, Arturo J. Aldama (editors), Encyclopedia of Latino Popular Culture, Volume 2, page 520, Today Plaza Garibaldi near the center of Mexico City is considered the home of mariachis, where mariachi musicians congregate in the plaza, waiting for patrons and tourists to audition them and invite them to perform. […] Mariachi Vargas de Tecalitlán has been considered the premier Mexican mariachi for nearly a century.

3. A member of such a group.

   The mariachis would serenade / and they would not shut up till they were paid.

   1959, “In Old Mexico”, Tom Lehrer (music)