quetzalli.

Headword: 
quetzalli.
Principal English Translation: 

the quetzal bird (a trogon with long green tail feathers); or, the feathers of the quetzal bird (see Karttunen and Molina)

IPAspelling: 
ketsɑlli
Alonso de Molina: 

quetzalli. pluma rica, larga y verde.
Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 89r. col. 2. Thanks to Joe Campbell for providing the transcription.

Frances Karttunen: 

QUETZAL-LI plumage of the quetzal bird, a trogon with long green tail feathers (Pharomachrus mocinno) / pluma rica, larga y verde (M).
Frances Karttunen, An Analytical Dictionary of Nahuatl (Norman: University of Oklahoma Press, 1992), 210.

Attestations from sources in English: 

quetzalli (noun) = a beautiful feather; fig., something precious or beautiful
Daniel Garrison Brinton, Ancient Nahuatl Poetry: Containing the Nahuatl Text of XXVII Ancient Mexican Poems (1877), 162.

niman ie ic auh iauh in quetzalteculotl, in quetzalli iuhquin xexelihutiuh = Then the quetzal-owl went, with the quetzal feathers waving.
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), 240.

ca huehueyntin yaotiacahuan catca quetzalpatzactli = great, brave warriors. The quetzal feather crest device was their insignia (central Mexico, early seventeenth century)
Codex Chimalpahin: Society and Politics in Mexico Tenochtitlan, Tlatelolco, Culhuacan, and Other Nahuatl Altepetl in Central Mexico; The Nahuatl and Spanish Annals and Accounts Collected and Recorded by don Domingo de San Antón Muñón Chimalpahin Quauhtlehuanitzin, eds. and transl. Arthur J. O. Anderson and Susan Schroeder (Norman: University of Oklahoma Press, 1997), vol. 1, 144–145.

quetzalaztatzontli, çā moca quetzalli, motquitica quetzalli = the heron-feather headdress full of quetzal feathers, entirely of quetzal feathers
(central Mexico, sixteenth century)
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.

Tictetezoa in chalchiuitl, ticoaoazoa in quetzalli. Inin tlatolli: itechpa mitoa: in aquin itla cenca tlazotli quitlacoa. = You scratch the jade, you tear apart the quetzal feather. This is said about someone who mutilates something precious.
Thelma D. Sullivan, "Nahuatl Proverbs, Conundrums, and Metaphors, Collected by Sahagún," Estudios de Cultura Náhuatl 4 (1963), 138–139.

In uel patlaaoac, in uel xopaleoac quetzalli. Inin tlatolli itechpa mitoaya: in uel tenonotza tlatoani , anozo pilli, anozo tecutlato = A very broad and very green quetzal plumage. This was said of the king, or noble, or a royal orator.
Thelma D. Sullivan, "Nahuatl Proverbs, Conundrums, and Metaphors, Collected by Sahagún," Estudios de Cultura Náhuatl 4 (1963), 160–161.

Auh in cioa: njman conpeoaltia, qujvica, qujtemovia in tonatiuh: quetzalapanecaiotica in qujvica, quetzalco in ietiuh, qujtlapechhvia = And the women then began; they carried, they brought down the sun. They carried it with a litter of quetzal feathers; it traveled in quetzal feathers; they provided it a support (central Mexico, sixteenth century)
Fr. Bernardino de Sahagún, Florentine Codex: General History of the Things of New Spain; Book 6 -- Rhetoric and Moral Philosophy, No. 14, Part 7, eds. and transl. Arthur J. O. Anderson and Charles E. Dibble (Santa Fe and Salt Lake City: School of American Research and the University of Utah, 1961), 163.

Attestations from sources in Spanish: 

Auh in Chimalli yuan matlacpoualli quetzalli ma za niuhtiyez yn piyal yezqui in Diego yuan Baptista yvan centetl coyotl ytzontecon yuan patactli zan no yuh mopiyaz Aun in ozomahtli ytlacayo yuan coxcox ytzontecon xiniz mochivaz cirios onpa monequiz Tecpanteopan San Pedro yc oc centetl quetzaltototzintli ycuitlapil yyahtlapal zan no yuhtiyez mopiyaz = Y el escudo y las doscientas plumas, que solo asi esten, las tendran Diego y Baptista; y la cabeza de un coyote, y el trigo asi se tendra; y el mono, que se parece humano; y la cabeza del faisan se deshara para que se hagan cirios que se necesitaran en la iglesia de San Pedro; otro pajaro pequeño con la cola de plumas verdes, asi estara, asi se tendra. (Tlaxcala, 1581)
Catálogo de documentos escritos en náhuatl, siglo XVI, vol. I (Tlaxcala: Gobierno del Estado de Tlaxcala y el Archivo Histórico del Estado de Tlaxcala, 2013), 275.

noquetzale = mi pluma preciosa [hablando del hijo] (centro de México, s. XVI)
Josefina García Quintana, "Exhortación de un padre a su hijo; texto recogido por Andrés de Olmos," Estudios de Cultura Náhuatl 11 (1974), 150–151.

Yhuan ce quetzalhuehuetl = Y una guitarra de pluma (Xochimilco, 1650)
Vidas y bienes olvidados: Testamentos en náhuatl y castellano del siglo XVII, vol. 3, Teresa Rojas Rabiela, et al, eds. (México: CIESAS, 2002), 248–249.

nicm[aca] tamasqua tilmahtli yuan cempoualli quetzalli = le dejo una manta llamada uayle antigua y veinte plumas verdes (Cholula, 1599)
Vidas y bienes olvidados: Testamentos indígenas novohispanos, vol. 2, Testamentos en náhuatl y castellano del siglo XVI, eds., Teresa Rojas Rabiela, Elsa Leticia Rea López, Constantino Medina Lima (Mexico: Consejo Nacional de Ciencias Tecnología, 1999), 322–323.

Auh centetl quetzallamamalli yntech nicpouhtiuh yn pipilti yc macehuazque yn iquac mitotizque yn iquac ilhuitl quiztiuh = Íten, una mesa [sic] se la dejo a los principales, para que les sirva en la fiesta del pueblo (Tetepango, Hidalgo, 1586)
Vidas y bienes olvidados: Testamentos indígenas novohispanos, vol. 2, Testamentos en náhuatl y castellano del siglo XVI, eds., Teresa Rojas Rabiela, Elsa Leticia Rea López, Constantino Medina Lima (Mexico: Consejo Nacional de Ciencias Tecnología, 1999), 266–267.

centetl quetçaleca ce huaztli monamacaz = un aventador de plumas ricas que se llaman quetzales, se ha de vender (San Juan Teotihuacan, 1563)
Vidas y bienes olvidados: Testamentos indígenas novohispanos, vol. 2, Testamentos en náhuatl y castellano del siglo XVI, eds., Teresa Rojas Rabiela, Elsa Leticia Rea López, Constantino Medina Lima (Mexico: Consejo Nacional de Ciencias Tecnología, 1999), 146–147.