iyo. guay. interjection. Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 36v. col. 2. Thanks to Joe Campbell for providing the transcription.
Frances Karttunen:
IYOH dolorous interjection / guay interjección (M) ((I)Bf.8v,(1)Rp.97). The glottal stop is attested only in R. Frances Karttunen, An Analytical Dictionary of Nahuatl (Norman: University of Oklahoma Press, 1992), 123.