The word “mariachi” was thought to have derived from the French word mariage (“marriage”), dating from the French intervention in Mexico in the 1860s, related to the music’s appearance at weddings. This was a common explanation on record jackets and travel brochures. This theory was disproven with the appearance of documents that showed that the word existed before this invasion.
The origin of the word is disputed, but prominent theories attribute it to indigenous roots. One states that it comes from the name of the wood used to make the dance platform. Another states that mariachi comes from the indigenous name of a tree called pilla or cirimo; yet another states that it came from an image locally called María H (pronounced Mari-Ache). In many Mexican cultures they are also called Marietti. Mariachi can refer to the music, the group, or just one musician. Wikipedia