tlacaxinachtli.

Headword: 
tlacaxinachtli.
Principal English Translation: 

semen or ovum, the human "seed" of a man or a woman (see Karttunen, Molina, and Sahagún)

Orthographic Variants: 
tlācaxināchtli
IPAspelling: 
tɬɑːkɑʃinɑːtʃtɬi
Alonso de Molina: 

tlacaxinachtli. simiente devaron o de muger.
Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 116r. col. 1. Thanks to Joe Campbell for providing the transcription.

Frances Karttunen: 

TLĀCAXINĀCH-TLI inalienably possessed form: -TLĀCAXINĀCHYŌ semen, human seed / simiente de varón o de mujer (M), el semen genital (C) [(1)Cf.83r]. M gives a derivation of this with –YŌ meaning ‘human generation, lineage’ and a plural form with –TIN for ‘first human generation, progenitors of the human race.’ See TLĀCA-TL, XINĀCH-TLI.
Frances Karttunen, An Analytical Dictionary of Nahuatl (Norman: University of Oklahoma Press, 1992), 253.

Attestations from sources in English: 

tlacaxinachtli = seed of man (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), 130.