xillantli.

Headword: 
xillantli.
Principal English Translation: 

belly, abdomen, womb, entrails (see Molina and Karttunen)

IPAspelling: 
ʃillɑːntɬi
Alonso de Molina: 

xillantli. vientre, o barriga.
Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 159r. col. 2. Thanks to Joe Campbell for providing the transcription.

Frances Karttunen: 

XILLĀN-TLI womb, belly / vientre o barriga (M) There is disagreement across sources on vowel-length patterning for this item. It is attested twice in B, both times with the vowel of the second syllable marked long, once with the first vowel specifically marked short. C follows suit once in marking the vowel of the second syllable long but in four other attestations leaves both vowels of the stem unmarked. T consistently has the reflex of a long vowel in the first syllable and a short vowel in the second, XĪLLAN-TLI. If the second element is the postposition –TLAN ‘beneath,’ the A should be short.
Frances Karttunen, An Analytical Dictionary of Nahuatl (Norman: University of Oklahoma Press, 1992), 325.

Attestations from sources in English: 

in aço imixquac, in anoço incuexcochtlan, anoço iniollopan, anoço imelchiquipan, anoço imitipan, in anoço vel inxillan = the forehead, the nape of the neck, the heart, the chest, the stomach, or the whole abdomen (Mexico City, 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), 146.

Texillan tetozcatlan oquiz. Inin tlatolli itechpa mitoaya in aquin itech oquiz tlatocamecayotl = From someone's entrails, from someone's throat, he came forth. This was said about the person who comes from nobility.
Thelma D. Sullivan, "Nahuatl Proverbs, Conundrums, and Metaphors, Collected by Sahagún," Estudios de Cultura Náhuatl 4 (1963), 148–149.

xillantli = abdomen;
tonecuelpachoaia = our place which doubles;
tonepuztequia = our place which breaks;
ninocuelpachoa = I double myself;
ninopuztequi = I break;
noxillã mococoa = I have a pain in the abdomen (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), 121.

themes: 
Anatomy