ilhuicatl.

Headword: 
ilhuicatl.
Principal English Translation: 

the celestial realm, heaven, sky (noun) (see also ilhuicac)

Orthographic Variants: 
ilhuicatli, ilhuicac, elhuicac, ylhuicac, yluicatl
IPAspelling: 
ilwikɑtɬ
Alonso de Molina: 

Ilhuicatl. cielo.
Ilhuicacayotica. celestialmente.
Ilhuicacayotl. cosa celestial.
Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, f. 37v.

ilhuicacopa. de hazia el cielo.
Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 37v. col. 1. Thanks to Joe Campbell for providing the transcription.

ilhuicatitech. enel cielo.
Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 37v. col. 1. Thanks to Joe Campbell for providing the transcription.

Frances Karttunen: 

ILHUICA-TL heaven, sky / cielo (M)
Frances Karttunen, An Analytical Dictionary of Nahuatl (Norman: University of Oklahoma Press, 1992), 104.

Lockhart’s Nahuatl as Written: 

sky, heaven, heavens. most often seen in the locative form ilhuicac. 220
James Lockhart, Nahuatl as Written: Lessons in Older Written Nahuatl, with Copious Examples and Texts (Stanford: Stanford University Press and UCLA Latin American Studies, 2001), 220.

Attestations from sources in English: 

in huel tehuatzin tiquinmochichihuili tiquinmoqualnextili. yn ilhuicame. yn inca in cicitlaltin yn ica in tonatiuh. yn ica yn metztli = You Yourself Who adorned and embellished the heavens with the stars, the sun, and the moon (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. 2, 140–141.

no ihuan niquimotlatlactilia mohtintzitzi quexquih Santtos ihuan Santas in onpa motemiltitiCate in ilhuiCac inic nopan Motlatoltitzinosque = and I also implore all the male and female saints that fill heaven to speak on my behalf (San Pedro Calimaya, Toluca Valley, 1758)
Caterina Pizzigoni, ed., Testaments of Toluca (Stanford: Stanford University Press and UCLA Latin American Center Publications, 2007), 190.

ilhuicatl ihtic = within the sky, heaven
Heaven was "a place of residence for God, angels, saints, and the souls of the virtuous dead."
Louise M. Burkhart, Holy Wednesday: A Nahua Drama from Early Colonial Mexico (Philadelphia: University of Pennsylvania Press, 1996), 195.

ilhuicatli ytlalticpa = heaven on earth
Robert Haskett and Stephanie Wood's notes from Nahuatl sessions with James Lockhart and subsequent research.

yn S,ⁿtoti Ycha S,ⁿtati. Yn motemiltitiCate Ylchuicaqui Calitiqui = the male and female saints who fill heaven (San Pablo Tepemaxalco, Toluca Valley, 1731)
Caterina Pizzigoni, ed., Testaments of Toluca (Stanford: Stanford University Press and UCLA Latin American Center Publications, 2007), 151.

Çatepan omomiquili otlamelauh yn ianimantzin inompa ylhuicac = after she died, her soul went directly to heaven (late sixteenth century, Central Mexico)
Louise M. Burkhart, Before Guadalupe: The Virgin Mary in Early Colonial Nahuatl Literature, Institute for Mesoamerican Studies Monograph 13 (Albany: University at Albany, 2001), 14.

xoxouhqui xicaltzintli, mumuchitl ontemi...tla ca nenca iluicatl. = a little blue-green jar filled with popcorn?...it is the sky.
Thelma D. Sullivan, "Nahuatl Proverbs, Conundrums, and Metaphors, Collected by Sahagún," Estudios de Cultura Náhuatl 4 (1963), 130–131.

yn quiteneuhtihui tachcocolhuan catca. tonatiuh quallo. ynic motlapololtiaya. canel amo huel oquimattiaque. yn quenin hui. yn quenin mochihua. ynic yzqui tlanepanoltitimani. yn ilhuicame ynic otlatoca. ynic momamallacachotihui. ynic mopapanahuitihui. ynic cecenteotlatoca. ynic yzqui tlanepanoltitimani. ylhuicame = our forefathers called it the sun being eaten, in which they were confused, for they did not know how the heavens go, how they are made, so that each one lies across the other as they go along revolving and crossing one another, how each one goes along, how each of the heavens crosses the others (central Mexico, 1611)
Annals of His Time: Don Domingo de San Antón Muñón Chimalpahin Quauhtlehuanitzin, James Lockhart, Susan Schroeder, and Doris Namala, eds. and transl. (Stanford: Stanford University Press, 2006), 178–9.

Attestations from sources in Spanish: 

in atl ca yuhquima yollo yn ilhuicatl = el agua es como el corazón del cielo (ca. 1582, Mexico City)
Luis Reyes García, ¿Como te confundes? ¿Acaso no somos conquistados? Anales de Juan Bautista (Mexico: Centro de Investigaciones y Estudios Superiores en Antropología Social, Biblioteca Lorenzo Boturini Insigne y Nacional Basílica de Guadalupe, 2001), 170–171.

totecuiyo Jesuxrispo ynic nechmotlaocolliliz nechmouiquilli ytlatocachantzinco yluicatl itec yc tlanequilli = [Nuestro Señor Jesucristo allá en el cielo y la gloria], me quiera perdonar y llevarme a su santo reino (Tizatlan, Tlaxcala, 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), 314–315.

themes: 
Celestial Phenomena
Religion (Indigenous Christianty)