Nahuatl (, with stress on the first syllable) is a language of the Nahuan branch of the Uto-Aztecan language family. It is spoken by an estimated 1.5 million Nahua people, most of whom live in Central Mexico. All Nahuan languages are indigenous to Mesoamerica.
Nahuatl has been spoken in Central Mexico since at least the 7th century AD. It was the language of the Aztecs, who dominated what is now central Mexico during the Late Postclassic period of Mesoamerican history. During the centuries preceding the Spanish conquest of Mexico, the Aztec Empire had expanded to incorporate most of Mexico, and its influence caused the variety of Nahuatl spoken by the residents of Tenochtitlan becoming a prestige language in Mesoamerica. At the conquest, with the introduction of the Latin alphabet, Nahuatl also became a literary language and many chronicles, grammars, works of poetry, administrative documents and codices were written in the 16th and 17th centuries. This early literary language based on the Tenochtitlan variety has been labeled Classical Nahuatl and is among the most studied and best documented languages of the Americas.
Today Nahuatl varieties are spoken in scattered communities mostly in rural areas throughout central Mexico. There are considerable differences among varieties, and some are mutually unintelligible. They have all been subject to varying degrees of influence from Spanish. No modern Nahuatl languages are identical to Classical Nahuatl, but those spoken in and around the Valley of Mexico are generally more closely related to it than those on the periphery. Under Mexico's Ley General de Derechos Lingüísticos de los Pueblos Indígenas ("General Law on the Linguistic Rights of Indigenous Peoples") promulgated in 2003, Nahuatl and the other 63 indigenous languages of Mexico are recognized as lenguas nacionales ("national languages") in the regions where they are spoken, enjoying the same status as Spanish within their region.
Nahuatl is a language with a complex morphology characterized by polysynthesis and agglutination (agglutinative language), allowing the construction of long words with complex meanings out of several stems and affixes. Through centuries of coexistence with the other indigenous Mesoamerican languages, Nahuatl has absorbed many influences, coming to form part of the Mesoamerican Linguistic Area.
Many words from Nahuatl have been borrowed into Spanish, and since diffused into hundreds of other languages. Most of these loanwords denote things indigenous to central Mexico which the Spanish heard mentioned for the first time by their Nahuatl names. English words of Nahuatl origin include "avocado", "chayote", "chili", "chocolate", "atlatl", "coyote", "axolotl" and "tomato".