Wordnet 3.0
NOUN (1)
1. 
 a percussion instrument that is made from a dried cactus branch that is hollowed out and filled with small pebbles and capped at both ends; 
 makes the sound of falling rain when tilted; 
 origin was in Chile where tribesmen used it in ceremonies to bring rain; 
WordNet (r) 3.0 (2006):
rain stick
    n 1: a percussion instrument that is made from a dried cactus
         branch that is hollowed out and filled with small pebbles
         and capped at both ends; makes the sound of falling rain
         when tilted; origin was in Chile where tribesmen used it in
         ceremonies to bring rain