bass drum

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A large drum having a cylindrical body and two heads and producing a low, resonant sound.

Wiktionary

1. n. a large drum with a low pitch

GNU Webster's 1913

1. (Mus.) The largest of the different kinds of drums, having two heads, and emitting a deep, grave sound. See bass, a.
2. n. See in the Vocabulary.

WordNet 3.0

1. n. a large drum with two heads; makes a sound of indefinite but very low pitch