Principal English Translation: 

a person's name (attested as male), a title, or perhaps a person affiliated with a place called Itzcotlan; the name clearly has something to do with obsidian (itztli)

Orthographic Variants: 
Yzcotecatl, Itzcotocatl, Izcotecatl
Attestations from sources in English: 

A famous man associated with Colhuacan was given the title "Itzcotecatl" according to Diego Durán.
Diego Durán, The History of the Indies of New Spain (1994), 99.

"ytoca yzcotecatl = named Itzcotocatl[?]" -- The vowel change here is copied precisely as published. (Cuernavaca region, ca. 1540s)
The Book of Tributes: Early Sixteenth-Century Nahuatl Censuses from Morelos, ed. and transl. S. L. Cline, (Los Angeles: UCLA Latin American Center Publications, 1993), 128–129.

"I, Pedro de Paz, councilman, interrogated the Palpan elders: the first Martín Tlacuchcalcatl,² the second Miguel Itzcotecatl...."
Beyond the Codices, eds. Arthur J. O. Anderson, Frances Berdan, and James Lockhart.

Another Juan Itzcotecatl is mentioned in a letter in Nahuatl of 1557.
Jan Szeminski, John Sullivan, and Justyna Olko, Dialogue with Europe, Dialogue with the Past: Colonial Nahua and Quechua Elites in Their Own Words (Boulder: University Press of Colorado, 2018), and see item #24;

Attestations from sources in Spanish: 

"Itzcotecatl, itzcoteca, de Itzcotlan. Le encontramos escrito silábicamente con itztli y comitl, haciendo Itz-co-tlan, 16, ó bien con solo el símbolo de la obsidiana, 16bis, que produce el sonido inicial."
Manuel Orozco y Berra, Historia antigua y de la conquista de México: 1.pte. (1880), 520.