The word chia came directly from its Nahuatl equivalent, namely chian, according to an online Nahuat dictionary. Wikipedia claims it's derived from chian "oily" but according to the dictionary, chiahuac is "oily", which feel like compounds with additional suffixes on top of the chia root. As chia seeds produces 25% to 30% oil, I think words with "oily" meaning in Nahuatl were actually derived from the root meaning the chia plant.
The Nahuatl glyph for chia looks like either a brown triangle or a half circle with dots inside, no doubt representing the dark grey chia seeds. However, there is also a variant in which the dots are replaced by conventional symbols of soil, such as the name Chiapan, which corresponds to Chiapas in modern times. Chiapas in fact means "above the river of chias" (http://geography.berkeley.edu/ProjectsResources/Glyphs/Plate12/Chiapan.html). However, a similar toponym, Teochiapan, does use the regular dotted variant (http://geography.berkeley.edu/ProjectsResources/Glyphs/Plate26/Teochiapan.html).
The chia glyph can also be used as a phonetic sign to write the chi syllable. One example of this usage comes from the Codex Xolotl, a book from the Texcoco region of Central Mexico written right after the Spanish conquest. It details the history of the Aztecs and especially the city of Texcoco, one of the three "allies" that made up the Triple Alliance aka the Aztec Empire. Like most Nahuatl manuscripts it is highly pictorial but a surprising amount of texts with phonetic spelling is used. A character named Achitometl, who was the king of the Tepanecs, has his name spelled out nearly phonetically as a-chi-(to)-me-e. For some reason the to syllable is missing, possibly because it served no grammatical function.
Also, take note of the syllabic glyph e, which is the black oval with a white smaller oval inside. Here it serves as a phonetic complement to reinforce the vowel of the last syllable. However, of interest is the fact that the syllabic glyph e is also the bean glyph, as "bean" in Nahuatl is etl. In fact, my wife said that's what's for dinner tomorrow, our approximation of the Costa Rican gallo pinto. However, instead of going into the wonderful world of beans, I shall stop here, and leave the exploration of another ancient staple for another day.
- Nahuatl Dictionary
- Byrne, Roger, et al, Nombres Geográficos de México, 1999
- Lacadena, Alfonso and Wichmann, Søren, Longitud vocálica y glotalización en la escritura náhuatl, Revista Española de Antropología Americana 38.2: 121-150, 2008