to trample something; or, to tamp something down (see Karttunen)
IPAspelling:
ʃihʃili
Alonso de Molina:
xixili. nitla. (pret. onitlaxixil.) pisar con pison, o henchir recalcando. Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 160r. col. 1. Thanks to Joe Campbell for providing the transcription.
Frances Karttunen:
XIHXIL(I) vt to trample something, to tamp something down / pisar con pisón, o henchir recalcando (M) [(1)Cf.91v]. Frances Karttunen, An Analytical Dictionary of Nahuatl (Norman: University of Oklahoma Press, 1992), 324.