(you can download a glossary for the Kindle here, courtesy of Nathan McKnight)
ahuizotl: beast living in Lake Texcoco, feasting on the eyes and fingernails of the dead.
calmecac: (lit. House of Tears) school where the children of the wealthy and those destined to the priesthood were educated.
calpulli: clan. In reality, a clan had both a geographical extent (the calpullis owned their land, and Tenochtitlan was split along the lines of calpulli lands), and a political and religious one (the elders of the calpulli were responsible for basic justice as well as for worship).
chinamitl: (also chinampa, Floating Garden): an artificial island used to grow crops.
She-Snake (cihuacoatl): Mexica equivalent to viceroy. Symbolising the female order, he was in charge of domestic affairs. When the Emperor went to war, the She-Snake ruled the city in his stead: the two of them never left Tenochtitlan at the same time.
iyac: (lit. Leading Youth): a warrior who has proved his worth in combat by taking a prisoner, either singly or in combat.
House of Youth: the counterpart to the calmecac. Trained warriors not of the nobility.
Knights: elite corps of warriors, reserved for those with strong prowess in battle. Includes the Jaguar Knights, the Eagle Knights and the Arrow Knights.
macuahitl (sword): a wooden club with embedded obsidian shards; the traditional Aztec weapon.
Master of the House of Darts: the House of Darts is an armoury (the darts referring to the throwing spears kept inside). There were actually several of these in the capital: one in the imperial palace, and three around the Sacred Precinct, at the entrance of the causeways that were the only link between Tenoctitlan and the land. The Master of the House of Darts was the commander of the armies, a step below the Revered Speaker himself. He coordinated the movement of troops, decided tactics, and planned the campaign once the Revered Speaker had decided to declare war on a city.
Mictlan: the Aztec underworld, destination of most of the dead. In Aztec mythology, those who had died in peculiar circumstances–battle, sacrifice, drowning or in childbirth, for instance–rejoined various heavens. The remainder went into Mictlan.
patolli: Aztec board game, played with beans as dice.
priests: the priestly hierarchy had various ranks, the lowest ones being those of priestly aspirants, and of calmecac students. Then came the novice priests, who served a particular god in a particular temple. With time, they could be promoted to offering priests. Those cults which offered human sacrifices had a higher rank: the fire-priests, responsible for choosing the victims and for lighting a fire in their chests. Finally came the High Priests.
Revered Speaker (tlatoani): Mexica Emperor
Triple Alliance: formed by the cities of Tenochtitlan, Texcoco and Tlacopan, the Triple Alliance was the main military body of the Valley of Mexico. A mostly military alliance, it had very few political realities: each city remained independent), but they sent joint armies, and shared in the tribute that came back.
tzin: Aztec honorific, equivalent to “Lord”. I have taken the liberty of using those as marks of reverence (much in the way of the Japanese “sama”), and not as actual titles.