citlalin popoca.

citlalin popoca.
Principal English Translation: 

a comet that lasts a long time (see Molina); a smoking star

Orthographic Variants: 
Alonso de Molina: 

citlalimpopoca. cometa que dura mucho tiempo.
Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 22v. col. 1. Thanks to Joe Campbell for providing the transcription.

Attestations from sources in English: 

The comet was seen as a negative omen for rulers, who might perish or become imprisoned, see war break out, or see a famine among the people.
Fr. Bernardino de Sahagún, Florentine Codex: General History of the Things of New Spain; Book 7 -- The Sun, Moon, and Stars, and the Binding of the Years, Number 14, Part 8, 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, 1953), 13.