xiuhquilitl.

Headword: 
xiuhquilitl.
Principal English Translation: 

a green herb; also a paste or cake for dyeing things blue/green (see Molina)

Alonso de Molina: 

xiuhquilitl. pastel para teñir.
Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 159v. col. 2. Thanks to Joe Campbell for providing the transcription.

Attestations from sources in English: 

Xiuhquilitl is said to be indigofera suffruticosa or indigofera anil, related to indigofera tinctoria, which produces most commercial indigo.
Safford, "Cosmos Sulphureus," Journal of the Washington Academy of Sciences 9 (1918), 614.