coatl.

Headword: 
coatl.
Principal English Translation: 

snake, serpent; twin, twins; also, a calendrical marker; also, a person's name (see Molina, Karttunen, and Lockhart)

Orthographic Variants: 
cohuatl, cohua, covatl, cuoatl
IPAspelling: 
koɑːtɬ
Alonso de Molina: 

coatl. culebra, mellizo, o lombriz del estomago.
Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 23r. col. 1. Thanks to Joe Campbell for providing the transcription.

Frances Karttunen: 

COĀ-TL pl: CŌCŌAH ~ CŌĀMEH snake, serpent, worm; twin / culebra, mellizo, o lombriz de estómago (M) This has two distinct senses, the concrete ‘snake’ and an abstract one involving reciprocity. This latter use is involved in the use of CŌĀ-TL to mean ‘twin,’ in the expression of a host-and-guest relationship in CŌĀNŌTZ(A), and in coatequitl ‘communal work’ (Which is not attested in the sources for this dictionary but is transparently a compound of CŌĀ-TL and TEQUI-TL ‘work’). There is no phonological contrast corresponding to the two different uses of CŌĀ-TL. Possibly the reciprocal sense derives from some belief about snakes. Otherwise there are two homophonous lexical items. Because the sequense is internal, it is impossible to determine if it should be ŌĀ or ŌHUĀ.
Frances Karttunen, An Analytical Dictionary of Nahuatl (Norman: University of Oklahoma Press, 1992), 36.

Lockhart’s Nahuatl as Written: 

perhaps it should be written cōhuātl; that the ō is long is dubious.
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), 215.

Attestations from sources in English: 

Cuix ticneltoca in temictli in Peyotl, Ololiuhqui, Tletl, Tecolotl, Chiquatli. coatl nozo itla oc centlamantli quimoteotiaya in mocolhuan huehuetque. = Do you believe in dreams, peyote, ololiuhqui, fire, owls, barn owls, snakes or some other thing your grandfathers the ancients used to worship?
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), 91.

Tecōātl, Cuauhcōātl = Stone-snake [i.e., rocky road], Wood-snake [i.e., mountain road]. (Atenango, between Mexico City and Acapulco, 1629)
Hernando Ruiz de Alarcón, Treatise on the Heathen Superstitions That Today Live Among the Indians Native to This New Spain, 1629, eds. and transl. J. Richard Andrews and Ross Hassig (Norman and London: University of Oklahoma Press, 1984), 92.

açompa tlamizque cohuaquallozque. ca cenca ychan yn cocohua = Perhaps they will come to an end there, eaten by snakes; for it is great snake country. (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, 92–93.

y nemi y yca ya chicvzivhtl y nemi ymomesti cvcvuha catca = The reason that both of them are now seven years old is that they were twins. (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.

ynic vmeti oquichtl omozivhauhti ayamo moquatequia ytoca cvuhatl = The second, male, married, not yet baptized, is named Coatl. (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.

oncan in quiminque ce covatl cenca tomahuac ce chichimecatl = There they shot a very thick snake with arrows; it was a Chichimeca who shot it.
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, 24–25.

cuoatl [sic] = Serpent, a name given boys (Central Mexico, sixteenth century)
Fray Bernardino de Sahagún, Primeros Memoriales, ed. Thelma D. Sullivan, et al. (Norman: University of Oklahoma Press, 1997), 253.

coatilmahtli = snake cape;
coatzontecomayo tilmahtli = the cape with the snake head design;
coaxayacayo tilmahtli = the cape with the serpent face design; it is mentioned in the Codice Florentino (CF X:186) as one of the costume items of the Huaxteca people
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), 185–186.

juo. coatl (Tepetlaoztoc, sixteenth century)
Barbara J. Williams and H. R. Harvey, The Códice de Santa María Asunción: Facsimile and Commentary: Households and Lands in Sixteenth-Century Tepetlaoztoc (Salt Lake City: University of Utah Press, 1997), 83.

loreço coatl = Lorenzo Coatl (the glyph next to the gloss for this name curiously does not show a serpent but rather a pot, comitl, and water, atl) (Tepetlaoztoc, sixteenth century)
Barbara J. Williams and H. R. Harvey, The Códice de Santa María Asunción: Facsimile and Commentary: Households and Lands in Sixteenth-Century Tepetlaoztoc (Salt Lake City: University of Utah Press, 1997), 98–99.

Hernando Cohuatl = a Mexica man who was arrested in Mexico City for protesting rising tributes in July 1564
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), 222–223.

Attestations from sources in Spanish: 

Cuix ticneltoca in temictli in Peyotl, Ololiuhqui, Tletl, Tecolotl, Chiquatli. coatl nozo itla oc centlamantli quimoteotiaya in mocolhuan huehuetque. = As creydo en sueños, en el Peyote, Ololiuque, en el fuego, en los Buhos, Lechusas, ò Culebras, &c. O en otros abusos que tuvieron tus antepasados.
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), 90–91.

Yn iquac ye omiqui nima ytec quicalaquique pipa yhuan cocohua tamaçolime caxtil mizto çaço nepapa yolcatl. = Una vez que murió, luego lo metieron dentro de una pipa junto con culebras, sapos, gallo, gato y cualquier otra variedad de animal. (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), 428–429.

axcan ypan xapato mo poa nahui cali tecpatl cali tochi acatl chihuitl cahuitl zipatli= ehecatl= cali= cuespali= cohuatl= miquistli= masatl= tochi= atl= iscuintli= osomatl= minali= acatl= ocelotl= quautli= coscaquautli= olin= tecpatl= quiahuitl= chochitl = ahoy en éste día sábado que se cuenta cuatro casa. Pedernal, Casa, Consejo, Caña, signos de los años en el Tiempo estos cuatro signos se cuentan. Lagarto, Mono, Viento, Yerba tocida, Casa, Caña, Lagartija, Tigre, Culebra, Aguila, Muerte, Aguila de collar, Venado, Movimiento, Conejo, Pedernal, Agua, Lluvia, Perro, Flor (Estado de Hidalgo, ca. 1722?)
Rocío Cortés, El "nahuatlato Alvarado" y el Tlalamatl Huauhquilpan: Mecanismos de la memoria colectiva de una comunidad indígena (New York: Hispanic Seminary of Medieval Studies, Colonial Spanish American Series, 2011), 34, 46-47.

ome tecontotonti tlatlacuilollo cohuatl = dos tecomates pintados que están en ellos una culebra pintada
Vidas y bienes olvidados: Testamentos en náhuatl y castellano del siglo XVII, vol. 3, Teresa Rojas Rabiela, et al, eds. (México: CIESAS, 2002), 242–243.