Tlacaxipehualiztli.

Headword: 
Tlacaxipehualiztli.
Principal English Translation: 

the name of a month of twenty days
James Lockhart, We People Here: Nahuatl Accounts of the Conquest of Mexico, Repertorium Columbianum v. 1 (Los Angeles: UCLA Center for Medieval and Renaissance Studies, 1993), 174, 178.

Chimalpahin placed it on about March 19–20 (about the Spring equinox) in his reckoning of the intersection with the Christian calendar (central Mexico, 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, 120–121.

Orthographic Variants: 
Tlacaxipeoaliztli, tlacaxipehualizti
Attestations from sources in English: 

19 Março Tlacaxipehualiztli = 19 March. Tlacaxipehualiztli. (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, 120–121.

ic vntetl metztli, in mjtoaia, tlacaxipeoaliztli = the second month, which was called Tlacaxipaualiztli; ...auh inic muchioaia, iquac miquja, yn ixqujch malli, yn ixqujch tlaaxitl, yn ixqujch haxioac = [it was] when all the captives died, all those taken in war
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), 46.

the second month, Tlacaxipeoaliztli, during which time blood sacrifices were made
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), 55.

themes: 
Gifts, Offerings, Sacrificial Rites
Religion (Indigenous)
Time, Calendar, Frequency
War, Conflict