xicolli.

Headword: 
xicolli.
Principal English Translation: 

a fringed, sleeveless jacket tied frontally
Justyna Olko, Turquoise Diadems and Staffs of Office: Elite Costume and Insignia of Power in Aztec and Early Colonial Mexico (Warsaw: Polish Society for Latin American Studies and Centre for Studies on the Classical Tradition, University of Warsaw, 2005), 103.

a male priest's ceremonial garment
See Mexicolore for a photo of a surviving example found at the Templo Mayor archaeological site: http://www.mexicolore.co.uk/aztecs/artefacts/xicolli

the center or navel of the universe; umbilicus
Gutierre Tibón, El ombligo como centro cósmico: Una contribución a la historia de las religiones (México: Fondo de Cultura Económica, 2014).

Orthographic Variants: 
xiculli
IPAspelling: 
ʃikoːlli
Attestations from sources in English: 

yoan xicolli, çan tlacuilolli in itenixio, hivitica tenpoçonqui = and a sleeveless jacket, painted all over, with eyes on its border and teased feathers at the fringe
James Lockhart, We People Here: Nahuatl Accounts of the Conquest of Mexico, Repertorium Columbianum v. 1 (Los Angeles: UCLA Center for Medieval and Renaissance Studies, 1993), 66.

conmaquiaya yn ixicol, ioã inpapalotilma yn imiyeteco. = They wore their xicolli and their butterfly capes, and [they had] their tobacco gourds.
Fray Bernardino de Sahagún, Primeros Memoriales, ed. Thelma D. Sullivan, et al. (Norman: University of Oklahoma Press, 1997), 62.

Sleeveless tunics (xiculli) are given as some of the essential items found in the "devil's houses."
Fray Bernardino de Sahagún, Primeros Memoriales, ed. Thelma D. Sullivan, et al. (Norman: University of Oklahoma Press, 1997), 117.

Naztauh, nomecaxicol. Quitoznequi: inic onechtequimacac in altepetl: ic in itlacauh oninochiuh intla niquitlacoz, intla itla ic nicouitiliz: nictzactiaz. = My heron-feather headdress, my jacket of ropes. This means: When the city gives me a responsibility I become a slave. If I hurt the city in some way, if I endanger it, I shall be put in jail.
Thelma D. Sullivan, "Nahuatl Proverbs, Conundrums, and Metaphors, Collected by Sahagún," Estudios de Cultura Náhuatl 4 (1963), 140–141.

When a tlatoani was invested in office, he was dressed in a green cape that had the same design of bones as that of the figure of Huitzilopochtli in the festival of Toxcatl. This was a festival in honor of Tezcatlipoca. Huitzilopochtli was identified with Tezcatlipoca. (central Mexico, sixteenth century)
Thelma Sullivan, "Tlatoani and tlatocayotl in the Sahagún manuscripts," Estudios de Cultura Nahuatl 14 (1980), 225–238. See esp. p. 229.

La Trinidad Xicolla (a place name) was part of the religious jurisdiction of Tacuba.
Emma Pérez Rocha, "Organización religiosa de la villa de Tacuba y sus cofradías rurales en el siglo XVIII," Dimensión Antropológica 4 (1995), 87-112, https://www.dimensionantropologica.inah.gob.mx/?p=1514

Attestations from sources in Spanish: 

"El xicolli era una camisa corta y sin mangas que se diferenciaba por un adorno, similar a una banda en el extremo inferior. Fue una importante prenda ritual en el Altiplano central, desde el Formativo Medio en Tlatilco, durante el Clásico en Teotihuacan y hasta la Colonia. Entre los mayas de las tierras bajas, en cambio, tanto en el Clásico como en el Posclásico Temprano, esta prenda se usó solamente como atuendo militar."
Patricia Rieff Anawalt, “Atuendos del México Antiguo”, Arqueología Mexicana, edición especial, núm. 19, pp. 10-19.

themes: 
Cardinal Directions, Cosmos
Textiles, Clothing