tzontli.

Headword: 
tzontli.
Principal English Translation: 

head of hair; or, a wrapped lock of hair on the top of the head, worn by priests and warriors; headdress; crest; and, by extention, sometimes just head
Part of this is from: 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.

also a number root for forming multiples of 400 (see examples, below);

and, one who has hair and fingernails can be a metaphor for a lord, tecuhtli (see examples below)

Orthographic Variants: 
çutli
IPAspelling: 
tsontɬi
Alonso de Molina: 

tzontli. cabello o pelo.
Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 153v. col. 2. Thanks to Joe Campbell for providing the transcription.

Frances Karttunen: 

TZON-TLI head of hair / cabello o pelo (M) Z has TZŌN, while all other sources have a short vowel. There is a variant TZOM(I)-TL recorded in S of which there is a possible, but ambiguous attestation in the sources for this dictionary. In compounds this sometimes has the sense of ‘hair’ and sometimes the sense of ‘head.’ See TZOM(I)-TL,
Frances Karttunen, An Analytical Dictionary of Nahuatl (Norman: University of Oklahoma Press, 1992), 318.

Attestations from sources in English: 

çan quauhpilli tequihua catca motzontlalpilliaya = He was only an eagle-noble, a seasoned warrior; he bound his hair. (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. 1, 118–119.

yn intzoncuetlax quitlalia mexica = the head leather that the Mexica put on (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. 1, 88–89.

ixtetenextique, tzoncoztique, tel cequi tliltic in intzon = their faces were the color of limestone and their hair yellow-reddish, though some had black hair (central Mexico, sixteenth century)
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), 80.

tlauhquecholtzontli = head ornament of the red spoonbill;
amatzontli itzpapalotl = a paper crown with obsidian butterflies (central Mexico, sixteenth century)
Justyna Olko, Turquoise Diadems and Staffs of Office: Elite Costume and Insignia of Power in Aztec and Early Colonial Mexico (Warsaw: Polish Society for Latin American Studies and Centre for Studies on the Classical Tradition, University of Warsaw, 2005), 154, 160–161.

totzon titlaveyaquilia = Our hair: We grow it long. (central Mexico, sixteenth century)
Fray Bernardino de Sahagún, Primeros Memoriales, ed. Thelma D. Sullivan, et al. (Norman: University of Oklahoma Press, 1997), 255.

tzontli = hair
xictzontli = hair about the navel
tzintzontli = hair of buttocks
ymaxtli (or imaxtli) = pubic hair
ixtzontli = hair of face
camatzontlil = hair of cheeks
nacaztzontli = hair of ear
cocotzontli = hair of throat
maztontli = hair of the hand
metztzontli = hair of the thigh
cotztzontli = hair of the calf of the leg
mapiltzontli = hair of the finger
xopiltzontli = hair of the toe
xocpaltzontli = hair of the foot
ciacatzontli = armpit hair
tentzontli = hair of chin
quexiltzontli = hair of groin (central Mexico, sixteenth century)
Fr. Bernardino de Sahagún, Florentine Codex: General History of the Things of New Spain; Book 10 -- The People, Part 11, 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, 1961), 137.

yquauhtzon = her headdress of eagle feathers (central Mexico, sixteenth century)
Fray Bernardino de Sahagún, Primeros Memoriales, ed. Thelma D. Sullivan, et al. (Norman: University of Oklahoma Press, 1997), 105.

y yaztatzon = his heron feather crest (central Mexico, sixteenth century)
Fray Bernardino de Sahagún, Primeros Memoriales, ed. Thelma D. Sullivan, et al. (Norman: University of Oklahoma Press, 1997), 108.

tlacochtzontli contlaliticac = he has placed a spear-shaft headdress on his head (central Mexico, sixteenth century)
Fray Bernardino de Sahagún, Primeros Memoriales, ed. Thelma D. Sullivan, et al. (Norman: University of Oklahoma Press, 1997), 113.

yz caten yn otyquizepuhque yi tequitque y zivatl yn piltotli yn telpochtli yn ichpochtli yn icnozivatli y ya mochi onçutli ynpa chicuetecpatli onmatlactli onnavi = Here are those whom we have added up: tribute payers, women, children, young men, young women, widows, a total of 974. (Cuernavaca region, ca. 1540s)
The Book of Tributes: Early Sixteenth-Century Nahuatl Censuses from Morelos, ed. and transl. S. L. Cline, (Los Angeles: UCLA Latin American Center Publications, 1993), 220–221.

In the Florentine Codex, Book 6, one finds the word for hair and the word for fingernail used as metaphors to refer to a newborn male child. (central Mexico, sixteenth century)
Fr. Bernardino de Sahagún, Florentine Codex: General History of the Things of New Spain; Book 6 -- Rhetoric and Moral Philosophy, No. 14, Part 7, 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, 1961), chapter 34, 183.

Intla vtlica qujntlaҫaltia in titici, in jnacaio mocioaquetzquj: vncan imjxpan contequjlia in jmapil in tlanepantla hicac: auh intla iooaltica vel qujtataca, no qujtequjlia in jmapil, ioan qujxima, qujcujlia in jtzon = If along the road they wrested the body of the mociuaquetzqui from the midwives, in their presence they cut off her middle finger. And if they could dig her up by night, they also cut off her finger and they clipped off, they took her hair from her (central Mexico, sixteenth century)
Fr. Bernardino de Sahagún, Florentine Codex: General History of the Things of New Spain; Book 6 -- Rhetoric and Moral Philosophy, No. 14, Part 7, 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, 1961), 162.

tzontle, iztitle: oticmjhijovilti, oticmociavilti: otijoculoc in vmeiocan in chicunauhnepanjuhca = O hair, O fingernail, thou hast endured fatigue, thou hast endured weariness; thou wert formed in the place of duality, [which is above] the nine heavens in tiers (central Mexico, sixteenth century)
Fr. Bernardino de Sahagún, Florentine Codex: General History of the Things of New Spain; Book 6 -- Rhetoric and Moral Philosophy, No. 14, Part 7, 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, 1961), 183.

in mach vel iehoantin in tzoneque, in jzteque in totecujiooan = it seemeth that verily these same who are possessors of hair, who are possessors of fingernails, are our lords (central Mexico, sixteenth century)
Fr. Bernardino de Sahagún, Florentine Codex: General History of the Things of New Spain; Book 6 -- Rhetoric and Moral Philosophy, No. 14, Part 7, 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, 1961), 186.

tzontle, iztitle = O hair, o fingernail (central Mexico, sixteenth century)
Fr. Bernardino de Sahagún, Florentine Codex: General History of the Things of New Spain; Book 6 -- Rhetoric and Moral Philosophy, No. 14, Part 7, 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, 1961), 141.

"...until the present day it is the custom among some of the Indians, and even others, in the city of Mexico to sell firewood by zontles of four hundred pieces. Twenty zontles, or eigth [sic] thousand make one xiquipilli, and three xiquipillis are equal to a carga or load, the which has twenty four thousand grains of cacao. To evade the trouble of counting so many when the merchandise was of considerable value, sacks of certain dimensions were used." (late nineteenth century, Mexico City)
Actas del Congreso Internacional de Americanistas, v. 11 (1897), 52.

iztetl tzontli = the hair, the nails = the offspring of someone important (central Mexico, sixteenth century)
Personal communication, James Lockhart, in sessions analyzing Huehuetlatolli.

Attestations from sources in Spanish: 

NEZAHUALCOYOTL ixiuhtzon ixiuhyacamiuh ixiuhtilma techilnahuayo itepotzoicpal = NEZAHUALCÓYOTL, su diadema de turquesas, su nariguera de turquesa como flecha, su manta color turquesa, festón rojo en la orilla, su asiento con espaldar (centro de México, s. XVI)
Víctor M. Castillo F., "Relación Tepepulca de los señores de México Tenochtitlan y de Acolhuacan," Estudios de Cultura Náhuatl 11 (1974), 183–225, y ver la pág. 208—209.

etzontli xivitl yvan caxtolpovali ypan epoval xivitl = mil quinientos sesenta (Cuauhtinchan, Puebla, s. XVI)
Luis Reyes García, "Ordenanzas para el gobierno de Cuauhtinchan, año de 1559," Estudios de Cultura Náhuatl 10 (1972), 272–273.

yetzonxihuitl = 1200 (Cuauhtinchan, Puebla, s. XVI)
Luis Reyes García, "Ordenanzas para el gobierno de Cuauhtinchan, año de 1559," Estudios de Cultura Náhuatl 10 (1972), 260–261.

themes: 
Anatomy
Numbers, Math