Y

the name of a mountain near the site of the shrine to Guadalupe; it was also called Mount Yoaltecatl; it was a site where child sacrifices (called "human banners," or tlacatetehuitl) were made to the rain deities

Fr. Bernardino de Sahagún, Florentine Codex: General History of the Things of New Spain; Book 2 -- The Ceremonies, No. 14, Part III, 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, 1951), 43.

paired with Yohualticitl, a part of a phrase said to a newborn baby: your mother, your father; or, male/female deities

(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), chapter 31, 171.

at night, by night (see Molina and Karttunen)

perhaps Bat Falcon, a bird (see Hunn, attestations)

nocturnal bird (see Molina; plural: yohualtotome)

a tree with medicinal value; its flowers open at night, hence its name, "Nocturnal Flower;" also called cozcaquahuitl and yahoalxochitl ("round flower") (Valley of Mexico, 1570–1587)
The Mexican Treasury: The Writings of Dr. Francisco Hernández, ed. Simon Varey, transl. Rafael Chabrán, Cynthia L. Chamberlin, and Simon Varey (Stanford: Stanford University Press, 2000), 122.

in the wee hours, or very early in the morning

very early in the morning, dawn

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), 242.