Castillan.

(a loanword from Spanish)

Headword: 
Castillan.
Principal English Translation: 

Castile, Spain
(a loanword from Spanish: Castilla)

Orthographic Variants: 
Caxtīllān, gastilan
Lockhart’s Nahuatl as Written: 

Caxtīllān. Spain. Sometimes written with s instead of x. reinterpreted Sp. loanword, from Castilla, Castile.
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), 213.

Attestations from sources in English: 

in texamatl, in ichamatl, quinamaca in castillã amatl = bark paper, maguey fiber paper. He sells Castilian paper. (central Mexico, sixteenth century)
Fr. Bernardino de Sahagún, Florentine Codex: General History of the Things of New Spain; Book 10 -- The People, No. 14, 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), 78.

noviyan altepetl ypan Ompa Castilla y noviyan Omonextitzino Oquimonexilili yvan miyecpa Oquinmoyolalilico ȳ nelli ytetlayecolticavan y nican tlalticapac = everywhere in the altepetls and over there in Spain. She revealed herself everywhere, showed herself to them, and many times she came to console her true servants here on earth (central Mexico, sixteenth century)
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), 134–135.

Nahuas of the sixteenth century seem to have concluded that Castilla would have had a locative suffix, -[t]lan. Thus, we see Castillan for Castilla, in many records. (central Mexico, sixteenth century)
See, for example, the discussion about this in 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), 6.

quimonpehualtique yn ocellome castillan = they sent two jaguars off to Spain (central Mexico, early seventeenth century)
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), 38–39.

Attestations from sources in Spanish: 

Inic centlamantli in momatiz, ca quenin motocayoz inin pahtli? Motoca: Tepitontepoztlaxcalli: castillancopa "Pastillas de fierro". = Por esto primera cosa que se sabrá es como se nombrará esta medicina Se llama tortillitas (pastillas) de fierro en castellano "pastillas de fierro". (centro de México, s. XVIII)
Neville Stiles, Jeff Burnham, James Nauman, "Los concejos médicos del Dr. Bartolache sobre las pastillas de fierro: Un documento colonial en el náhuatl del siglo XVIII," Estudios de Cultural Náhuatl 19 (1989), 269–287, ver página 280.

donya Ysabel Castilaxochitl = doña Ysabel Rosa de Castilla (San Salvador Tlalnepantla, 1618)
Vidas y bienes olvidados: Testamentos en náhuatl y castellano del siglo XVII, vol. 3, Teresa Rojas Rabiela, et al, eds. (México: CIESAS, 2002), 100–101.

yoan nahui tomines yc mocohuaz Castillan tlaxcalli = y cuatro tomines con que se comprepan de Castilla (San Juan Teotihuacan, 1563)
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), 144–145.

ynonamictzin ytoca Maria Castilanxochitl = mi mujer María Caxtilanxochitl
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 (Santa Bárbara, Tamasolco, Ocotelulco, Tlaxcala), 308-309.

ompovali gastilan totolim = cuarenta gallinas
Nuestro pesar, nuestra aflicción / tunetuliniliz, tucucuca; Memorias en lengua náhuatl enviadas a Felipe II por indígenas del Valle de Guatemala hacia 1572, introduction by Cristopher H. Lutz, paleography and translation by Karen Dakin (México: UNAM and Centro de Investigaciones Regionales de Mesoamérica, 1996, 56-57.

ompeuh in visitador ynic ya Castilla[n] = partió el visitador para irse a Castilla (ca. 1582, México)
Luis Reyes García, ¿Como te confundes? ¿Acaso no somos conquistados? Anales de Juan Bautista (Mexico: Centro de Investigaciones y Estudios Superiores en Antropología Social, Biblioteca Lorenzo Boturini Insigne y Nacional Basílica de Guadalupe, 2001), 142.