xictli.

Headword: 
xictli.
Principal English Translation: 

navel, bellybutton, umbilical cord; also, peephole (see Karttunen); possibly also a compass used for finding the right direction (?) (see Molina)

IPAspelling: 
ʃiːktɬi
Alonso de Molina: 

xictli. ombligo, o bruxula para tirar derecho.
Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 159r. col. 1. Thanks to Joe Campbell for providing the transcription.

Frances Karttunen: 

XĪC-TLI navel; peephole / ombligo o brujula para tirar derecho (M).
Frances Karttunen, An Analytical Dictionary of Nahuatl (Norman: University of Oklahoma Press, 1992), 324.

Attestations from sources in English: 

aço nauhmapa. in motzimani. auh nimã ye ic ompeua in tiacaua ỹuicpa õuetzi [onhuetzi] in tototecti q'moncotonilia in inxic = Perhaps they faced each other in the four directions. And then the chieftains started forth and fell upon the tototecti; they tickled their navels. (central Mexico, sixteenth century)
Fr. Bernardino de Sahagún, Florentine Codex: General History of the Things of New Spain; Book 8 -- Kings and Lords, no. 14, Part IX, 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, 1951), 85.

Tiacaoane xioalhvian [xihualhuian], xicxicvenquaquj [xicxichuenquaqui] in iautl [yaotl] = "O valiant warriors, come, eat the umbilical cord offering of Yaotl." (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), 204.

Ayac xictli in tlalticpac. Ayac tictoxictizque = No one on earth is an umbilical cord. (There is a play on words here: xictli, umbilical cord, and xictia, to look down upon someone.) We should not sneer at anyone.
Thelma D. Sullivan, "Nahuatl Proverbs, Conundrums, and Metaphors, Collected by Sahagún," Estudios de Cultura Náhuatl 4 (1963), 98–99.

Auh in ticitl: njman ie ic qujxictequj in piltzintli, qujcujlia in jxic: auh qujtlaxilia in qujlhvia inantzin, injc mapantivitz piltzintli, injc oalqujmjliuhtiuh: injn qujtoca xomolco: auh in jxic piltzintli pialilo tetzoloatzalo: qujn iaoc concaoa = And the midwife forthwith cut the umbilical cord of the baby; she took its umbilical cord. And she removed that which is called its afterbirth in which the baby came wrapped, in which it came enveloped. This she buried in a corner [of the house]. But the umbilical cord of the baby was saved. It was dried; later it was left in the battlefield [if it was the umbilical cord of a boy] (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), 169.

auh in jxic intech qujcaoaia tequjoaque, in iaoc matinj: injc vmpa qujtocazque in jxtlaoatl ijtic, in vncan muchioia iaoiotl: iuh qujlviaia in ca novian vel iaoqujҫaz. Auh in jxic cioapiltontli: ҫan vncan in calitlecujllan qujtocaia ixic: ic qujnezcaiotiaia: ca in cihoatl, acampa iaz: ҫan vel itequjuh in calinemjliztli, in tletitlan, in metlatitlan nemjliztli = And she entrusted his umbilical cord to the distinguished warriors, those wise in war, to bury it there in the midst of the plains where warfare was practised. So she told him he might issue forth in war in all parts. And the umbilical cord of the baby girl she only buried there by the hearth; thus she signified that the woman was to go nowhere. Her very task was the home life, life by the fire, by the grinding stone (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), 171.

Niman ic tlecujllan, qujtoca in ticitl, in jxic cioapiltzintli: qujl ic qujnezcaiotia, acampa ianj in cioatzintli: ҫan vel calitic, inemja, ҫan vel calitic ichan, amo monequj in campa iaz: ioan quitoznequj, vel itequjuh, in atl, in tlaqualli: achioaz, tlaqualchioaz, teciz, tzaoaz, hiqujtiz = Then the midwife buried the umbilical cord of the noblewoman by hearth. It was said that by this she signified that the little woman would nowhere wander. Her dwelling place was only within the house; her home was only within the house; it was not necessary for her to go anywhere. And it meant that her very duty was drink, food. She was to prepare drink, to prepare food, to grind, to spin, to weave (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), 173.

njman qujcujteoa in jxic iven piltontli, qujmotlalochtia, qujquâquativi = Then they took up the umbilical cord offering of the baby; they snatched it and ran; they went off eating it (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), 204.

xictli = navel;
comoltic = hollowed;
tiltic = possessing an eminence;
topoltic = like a little fish;
metlapiltic = like a mano;
quizqui = protruding
quiҫa = it protrudes
tôpoliui = it becomes like a little fish
metlapiliui = it becomes like a mano
caxiui = it becomes bowl-like
comoliui = it becomes hollowed
xicatlacomolli = navel hole
coiaoac = enlarged
vecatla = deep
coiaoa = it enlarges
uecatlaniui = it deepens
xicteuilacachiuhiantli = navel's roundness
iaoaltic = round
teuilacachtic = round
uecatlan = deep
pepeltic = like a round top
pepeliui = it becomes round like a top
teuilacachiui = it becomes round
uecatlaniui = it becomes deep
iaoaliui = it becomes round (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.

Attestations from sources in Spanish: 

Alzate nombra 'chiquis' a la hornilla, término que en la actualidad no reconocemos y que seguramente se deriva del náhuatl xi:ctli, 'ombligo.'
Carlos Sánchez Silva y Alejandro de Avila Blomberg, La grana y el nopal en los textos de Alzate (Mexico: Consejo Nacional para la Cultura y las Artes, Dirección General de Culturas Populares e Indígenas/CONACULTA, 2005), 61.