yacapantli.

Headword: 
yacapantli.
Principal English Translation: 

first born, eldest (see Molina and Karttunen)

IPAspelling: 
yɑkɑpɑntɬi
Alonso de Molina: 

yacapantli. primogenito, o primogenita.
Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 30r. col. 2. Thanks to Joe Campbell for providing the transcription.

Frances Karttunen: 

YACAPAN-TLI someone firstborn / primogénito o primogénita (M) [(2)Cf.125v, (2)Tp.134,227]. This appears in C only as an element of two compounds. T only has it prefixed with TĒ-, but M has it both without the prefix and as tiacapan with the vowel of TĒ– reduced. See –YACAPAN.
Frances Karttunen, An Analytical Dictionary of Nahuatl (Norman: University of Oklahoma Press, 1992), 333.

Attestations from sources in English: 

The construction noyacapan does not necessarily refer to the first born, but can mean "in my nose." And noyac can mean "my nose."
Thelma Sullivan, Compendio de la gramática náhuatl, 4a. edición (México: UNAM, 1998), 139.

themes: 
Family, Kinship, Descent