Principal English Translation:
to spring up; to bubble up; to boil; can refer to clouds and the weather (see Molina and Karttunen)
Alonso de Molina:
moloni. (pret. omolon.) manar la fuente o cosa assi. oleuantar se muchas nuues, o leuantarse con el ayre las plumas, o estenderse y oler mucho los perfumes y olores suaues.
Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 58v. col. 1. Thanks to Joe Campbell for providing the transcription.
Frances Karttunen:
MOLŌN(I) to waft, to rise and drift on air currents, to effervesce / manar la fuente o cosa así o levantarse muchas nubes, o levantarse con el aire las plumas, o extenderse o oler mucho los perfumes o olores suaves (M) [(1)Cf.74V, (2)Tp.141,150, (3)Zp.67,170].
Frances Karttunen, An Analytical Dictionary of Nahuatl (Norman: University of Oklahoma Press, 1992), 151.
Lockhart’s Nahuatl as Written:
atl nenez molon = water appeared and sprang up (17th c., central Mexico)
James Lockhart, Nahuatl as Written: Lessons in Older Written Nahuatl, with Copious Examples and Texts (Stanford: Stanford University Press and UCLA Latin American Studies, 2001), 86–87.
for water to spring and bubble up, for fog to rise, etc. Class 2: ōmolōn.
James Lockhart, Nahuatl as Written: Lessons in Older Written Nahuatl, with Copious Examples and Texts (Stanford: Stanford University Press and UCLA Latin American Studies, 2001), 225.
Attestations from sources in English:
In icoac tepeticpac moloni, momoloca, motlatlalia, mopiloa: mitoaia, ca ie uitze in tlaloque, ie quiiauiz, ie pixauizque in aoaque. = When clouds billowed and formed thunderheads, and settled and hung about the mountain tops, it was said: “The Tlalocs are already coming.
Now it will rain. Now the masters of the rain will sprinkle water."
Todd Olson, "Clouds and Rain," Representations 104:1 (Fall 2008), 102–115; quote, from the Florentine Codex, appears on 102.