Nagual

Nagual or Nahual (both pronounced [na'wal]) is a word used in the study of the religion, mythology, folklore and anthropology of Mesoamerican peoples and which is used with different definitions. It is related to the concept that certain persons are able to take on animal forms, which is present in many Mesoamerican cultures. It is also related to the equally common concept in Mesoamerican cultures of all persons having an animal companion to whom they are spiritually linked throughout their lives. The most common usage within Mesoamerican anthropology is to call Nagual a person who has a particularly strong animal companion and who uses this companion to cause harm to others, or who himself changes shape into animals in order to cause harm to others. The normal practice is to refer to the animal companion itself as a Tonal, following the Aztec practice.
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n. sorcerer, magician, enchanter

[Aztec] An Aztec tutelary spirit in the shape of an animal or a plant. Every god and human has his personal Nagual with whom he shares his fate until death. The Nagual of, for instance, Huitzilopochtli is a hummingbird and that of Quetzalcoatl is a feathered snake.

Nagal (Quiche) Usually rendered Nagual by the early Spaniards; title of the chief priest of the Quiches.