cihua tlayelli.

Headword: 
cihua tlayelli.
Principal English Translation: 

a woman's period, menstruation(?); tlayelli also refers to bloody diarrhea

Orthographic Variants: 
ciua tlayelli, cihua tlaelli, ciua tlaelli
Alonso de Molina: 

ciua tlayelli. las pares de la muger.
Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 22v. col. 2. Thanks to Joe Campbell for providing the transcription.

Attestations from sources in English: 

the placenta
Lucien Adam, et al, Bibliothèque linguistique Américaine, originally Coleccion lingüística Americana or Collection linguistique Américaine (Paris: Maisonneuve, 1871), 126.

Tlayelli (also tlaelli) relates to dirt, stain. It also stood for bloody diarrhea. And a placenta was also called tlayzllotl, "foulness."
Louise Burkhart, Slippery Earth, appendix.