to have big droplets fall when it rains (see Molina); for rain to sprinkle, to patter in large drops (see Karttunen)
IPAspelling:
tʃɑtʃɑpɑːni
Alonso de Molina:
chachapani. (pret. ochachapan.) caer gotas grandes quando llueue. Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 19r. col. 1. Thanks to Joe Campbell for providing the transcription.
Frances Karttunen:
CHACHAPĀN(I) for rain to sprinkle, patter in large drops / caer gotas grandes cuando llueve (M) [(2)Zp.111,150] redup. CHAPĀN(I) Frances Karttunen, An Analytical Dictionary of Nahuatl (Norman: University of Oklahoma Press, 1992), 44.