tlaco.

Headword: 
tlaco.
Principal English Translation: 

half, middle, center (see Karttunen and attestations); see also our entry for "tlacoton" ("little half"); also, a person's name, based on birth order (especially common for girls), Tlaco

Orthographic Variants: 
tlacol, thlacv
IPAspelling: 
tɬɑhko
Frances Karttunen: 

TLAHCO middle, center, half / mediano, que ocupa el centro, que está a la mitad, en medio (S). The first element of this contrasts with TLĀC-TLI ‘torso’ in vowel length as well as final consonant, despite the affinity of meaning. M has this in compounds involving ‘middle’ but not as an independent entry, it contrasts with TLACŌ-TL ‘staff, pole’ and TLĀCOH-TLI ‘slave’. T has also TLAHTLAHCO with the same sense.
Frances Karttunen, An Analytical Dictionary of Nahuatl (Norman: University of Oklahoma Press, 1992), 260.

Attestations from sources in English: 

yc ypan macuilli ypan tlaco hora = it was half past 5 o'clock (central Mexico, 1612)
Annals of His Time: Don Domingo de San Antón Muñón Chimalpahin Quauhtlehuanitzin, James Lockhart, Susan Schroeder, and Doris Namala, eds. and transl. (Stanford: Stanford University Press, 2006), 206–207.

centlacol yc onvc oquichtli centlacol yc vnoc in çivatl = one half who were there for it were men, one half were women
Fray Bernardino de Sahagún, Primeros Memoriales, ed. Thelma D. Sullivan, et al. (Norman: University of Oklahoma Press, 1997), 228.

oqualoc donali san tlaco = There was a solar eclipse, only half a one
Here in This Year: Seventeenth-Century Nahuatl Annals of the Tlaxcala-Puebla Valley, ed. and transl. Camilla Townsend, with an essay by James Lockhart (Stanford: Stanford University Press, 2010), 188–189.

tlaco oratica = half an hour
Here in This Year: Seventeenth-Century Nahuatl Annals of the Tlaxcala-Puebla Valley, ed. and transl. Camilla Townsend, with an essay by James Lockhart (Stanford: Stanford University Press, 2010), 190–191.

ytoca thlacv = named Tlaco (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), 118–119. There are many, many additional examples of the use of the name Tlaco in these demographic records.

Women's birth order names seem to relate from beliefs about female deities or goddesses linked to Tlazolteotl (also known as Ixcuina), who loved luxury and was lustful. The four sisters were Tiacapan (the oldest sister), then Teicu (the second oldest), the third was Tlaco (middle sister), and the youngest was Xoco, or "Xocutzin." Many girls bore these names. (central Mexico, sixteenth century)
Fr. Bernardino de Sahagún, Florentine Codex: General History of the Things of New Spain; Book 1 -- The Gods; No. 14, Part 2, 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, 1950), 8.

Attestations from sources in Spanish: 

opa mopia Santa Elenan nocentzin tlaco cuezcomatl = medio cuezcomate de mazorca se guarde en Santa Elena (Santa Bárbara)
Vidas y bienes olvidados: Testamentos indígenas novohispanos, vol. 1, Testamentos en castellano del siglo XVI y en náhuatl y castellano de Ocotelulco de los siglos XVI y XVII, eds. Teresa Rojas Rabiela, Elsa Leticia Rea López, y Constantino Medina Lima (Mexico: CIESAS, 1999), 236-237.

peuhqui tlapayahuitl ytlacotian agosto huel miec huehuezque caltin yhuan huel miec matoctin yhuan quicauh Çahuatl anrieostin aocmon huel panohuaya = Empezó la lluvia intensa a mediados de agosto. Se cayeron muchas casas y muchas se anegaron. Los arrieros dejaron el río Zahuatl porque no lo podían cruzar. (Tlaxcala, 1662–1692)
Juan Buenaventura Zapata y Mendoza, Historia cronológica de la Noble Ciudad de Tlaxcala, transcripción paleográfica, traducción, presentación y notas por Luis Reyes García y Andrea Martínez Baracs (Tlaxcala y México: Universidad Autónoma de Tlaxcala, Secretaría de Extensión Universitaria y Difusión Cultural, y Centro de Investigaciones y Estudios Superiores en Antropología Social, 1995), 284–285.

themes: 
Children, Childhood, Adolescence
Family, Kinship, Descent
Names (for people, deities)
Numbers, Math
Time, Calendar, Frequency
Women, Men, Gender