Principal English Translation: 

our mother, from nantli, possessed and with a reverential suffix; a term that was often used for the Virgin Mary but had also been used to refer to various goddesses (as tonan or tonantzin)

Orthographic Variants: 
Attestations from sources in English: 

This expression was often used for the Virgin Mary and, by extension, can be seen in reference to the Church. Its use concerned Sahagún, who wished people would refer to Mary as the mother of god. Tonantzin may have been used in reference to one or more pre-Columbian goddesses or divinities. In the Florentine Codex it is used once in this way, when a midwife uses the term in conjunction with the deity names Cihuacoatl and Quilaztli. But, even then, it was not meant as a deity name, but as a way of referring to a female, mother figure with respect.
Louise M. Burkhart, Before Guadalupe: The Virgin Mary in Early Colonial Nahuatl Literature, Institute for Mesoamerican Studies Monograph 13 (Albany: University at Albany, 2001), 11.

A ca nelle axcan, anqujmonochilia, anqujmotzatzililia, anqujticinotza in teteu innan: in tonan in iooalticitl, in qujtqujtica, in jmac ca, in jpial in xochicalli, in tlalticpac mjtoa temazcalli = For verily now ye cry out, ye call to summon Ticitl, the mother of the gods, Tonan, Yoalticitl, who governeth - in whose hands, in whose charge is - the xochicalli, which on earth is called 'sweatbath' (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), 153.