Amacozatl.

Headword: 
Amacozatl.
Principal English Translation: 

the name of a river in the hot lands
A. Wimmer, citing Sahagún and Garibay, in the Gran Diccionario Náhuatl, https://gdn.iib.unam.mx/diccionario/amacozatl/40492

the name of a barrio (also spelled Amacotzac) near Cohuixco (presumably near the river, too)
Pilar Maynez, El calepino de Sahagún: Un acercamiento (2014), referring to book 11, f. 224. Maynez translated Amacotzac as "En el Arcoiris."

Orthographic Variants: 
amacotzatl, amacotzac
See also: 
amacozcatl.