xihuitl.

Headword: 
xihuitl.
Principal English Translation: 

turquoise; herbs (sometimes psychedelic) and other greenish things, such as grass, greenstone; Lockhart says this word and the word for year are "possibly two words of different origin and same shape," so each will have its own entry in this dictionary
James Lockhart, Nahuatl as Written: Lessons in Older Written Nahuatl, with Copious Examples and Texts (Stanford: Stanford University Press and UCLA Latin American Studies, 2001), 241. And see other sources, below.

Attestations from sources in English: 

yeçe ca quenmanian, onicneltocac in temictli, in xiuhtzintli in peyotl in ololiuhqui? Yhuan in oc cequi tlamantli. = but at times I have believed in dreams, herbs, peyote and ololiuhqui, and other things (central Mexico, 1634)
Bartolomé de Alva, A Guide to Confession Large and Small in the Mexican Language, 1634, eds. Barry D. Sell and John Frederick Schwaller, with Lu Ann Homza (Norman: University of Oklahoma Press, 1999), 9.

yehica ypan ycuiliuhtica yn teotlatolli y nepapan xihuitl yn çacapahtli = because in holy scripture are written the various herbs and "grass medicines" (Central Mexico, 1552)
Fray Alonso de Molina, Nahua Confraternities in Early Colonial Mexico: The 1552 Nahuatl Ordinances of fray Alonso de Molina, OFM, ed. and trans., Barry D. Sell (Berkeley: Academy of American Franciscan History, 2002), 84–85.

ioan quixima, quichiqui in xivitl, in teuxi[vi]tl in incozqui, in incuecueioch in inpipilol = They also shave and scrape turquoise, fine turquoise, to be their necklaces, earrings and pendants. (Tlatelolco, 1540–80)
James Lockhart, Nahuatl as Written: Lessons in Older Written Nahuatl, with Copious Examples and Texts (Stanford: Stanford University Press and UCLA Latin American Studies, 2001), 195.

Attestations from sources in Spanish: 

yn chalchihuitl yhuan yn xihuitl = y los chalchihuites y las hierbas (Xochimilco, 1577)
Vidas y bienes olvidados: Testamentos indígenas novohispanos, vol. 2, Testamentos en náhuatl y castellano del siglo XVI, eds., Teresa Rojas Rabiela, Elsa Leticia Rea López, Constantino Medina Lima (Mexico: Consejo Nacional de Ciencias Tecnología, 1999), 210–211.

Ynin pintura Cotzatzin tezcacoatl ypiltzin siuhcozcatl apanecateuctli oncan otlacat don Alonso de Castañeda toxiuhtzaca = Esta pintura es del tezcacoatl Cotzatzin, hijo del apanecateuhctli Xiuhcozcatl, del cual nació don Alonso de Castañeda, el que cierra nuestra [cuenta de] años. (Quauhtinchan, s. XVI)
Historia Tolteca-Chichimeca, eds. Paul Kirchhoff, Lina Odena Güemes, y Luis Reyes García (México: CISINAH, INAH-SEP, 1976), 131.

themes: 
Colors
Dreams, Visions
Plants, Trees, Flora
Turquoise, Greenstone/Jade