drum major

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A man who leads a marching band or drum corps, often twirling a baton.

Century Dictionary and Cyclopedia

1. n. The chief or first drummer of a regiment.
2. n. One who directs the evolutions of a band or drum-corps in marching.
3. n. A riotous evening assembly. See drum, 9.

Wiktionary

1. n. One who conducts and commands a marching band.

GNU Webster's 1913

1. The chief or first drummer of a regiment; an instructor of drummers.
2. U.S. The marching leader of a military band.
3. A noisy gathering. [R.] See under Drum, n., 4.

WordNet 3.0

1. n. the leader of a marching band or drum corps