Synonyms for Rain (same or very similar meaning)
WordNet sense 1 (drops of fresh water that fall as precipitation from clouds):
rainwaterWordNet sense 2 (water falling in drops from vapor condensed in the atmosphere):
rainfallWordNet sense 3 (anything happening rapidly or in quick successive):
peltingWordNet sense 4 (precipitate as rain):
rain downFrom the ODE community, based on WordNetadd/edit