Brazilian musical bows of African origin, with a single wire string and sometimes a coconut or gourd resonator, held against the chest during play. One hand holds the bow and occasionally applies a metal coin to the string to alter its pitch, while the other strikes it with a stick; normally the striking hand holds or has attached to it a rattle.
Source: Art & Architecture Thesaurus
http://vocab.getty.edu/page/aat/300215572
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