ḍamaru (Sanskrit). A small hourglass-shaped double-headed drum having two hemispheres of wood or human crania with two clappers attached on strings. When twirled, the drum emits a sharp rattling sound, often said to create a sense of urgency in the face of all-pervading impermanency. It is widely used in Tibetan Buddhist tantric rituals and meditations, with a large ḍāmaru specified for use in chöd practice.

A Dictionary of Buddhism, Oxford University Press, 2003, 2004 (which is available in electronic version from answer.com)

ḍamaru (m. L.) id. Rājat. ii, 99 Prab.iii, 14

• surprise L.

Sanskrit-English Dictionary, by M. Monier William