xiuhhuitzolli.

Xihuitzolli is a shorter version of the same word. The spelling xinvitzolli appears in the Florentine Codex, Book 12, 28v, but James Lockhart has pointed out (in We People Here) that the "n" is intrusive.

Olko believes copilli is not the turquoise mosaic diadem that some have argued, but rather, that the turquoise mosaic diadem is the xiuhhuitzolli.
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), 114.

in tetepeiotl, in xivitzolli, in matemecatl, in cotzeoatl, in nacochtli, in tentetl, in tlalpilonj = the peaked cap, the turquoise diadem, the arm band, the band for the calf of the leg, the ear plug, the lip rod, the head band (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), 57.

"xiuhitzolli" (an orthographic variant) = crown with precious stones, according to W. S. Wilcox. Wilcox elaborates: "Molina has xiuhuitzolli, crown with precious stones. This has to be xiuh-uitzolli, since he always uses simple u/v for w- (and -uh for -w). A verb huitzoa is attested in yacauitzoa--to sharpen a point. This would give huitzo:lli for something pointed, presumably also something with points, i.e. a crown."
W. S. Wilcox, Nahuat-L posting, May 20, 2008.

Olko believes copilli is not the turquoise mosaic diadem that some have argued, but rather, that the turquoise mosaic diadem is the xiuhhuitzolli.
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), 114.

ca oconcujc in tepeiotl, in xiuhvitzolli, in matacaxtli, in matemecatl, in cotzeoatl, in tentetl, in nacochtli = for he hath taken the peaked cap, the turquoise diadem, the maniple, the wrist band, the leather band about the calf of the leg, the lip plug, the ear plug (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), 19.