trombone

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A brass instrument consisting of a long cylindrical tube bent upon itself twice, ending in a bell-shaped mouth, and having a movable U-shaped slide for producing different pitches.

Century Dictionary and Cyclopedia

1. n. A large musical instrument of the trumpet family. It has a long tube twice bent upon itself, and one of the loops is double, so that the outer tube, or slide, can be slipped over the inner like a sheath. When the slide is extended, the length of the tube is increased and its proper tone lowered. Since a full set of harmonics can be produced from any of many positions of the slide, the compass is long, and the intonation may be made very precise. The tone is peculiarly rich and solemn. Exceedingly fine harmonic effects may be produced by combining trombones of different sizes and fundamental pitches, which are called alto, tenor, and bass trombones respectively. The trombone is thought to have been known in ancient times. It is now a regular constituent of the orchestra and of the military band. For the latter it is sometimes made with valves or keys instead of a slide, but its characteristic tone and its flexibility of intonation are thus lost.

Wiktionary

1. n. A musical instrument in the brass family, having a cylindrical bore, and usually a sliding tube (but sometimes piston valves, and rarely both). Most often refers to the tenor trombone, which is the most common type of trombone and has a fundamental tone of B♭ˌ (contra B♭).
2. n. The common European bittern.

GNU Webster's 1913

1. n. (Mus.) A powerful brass instrument of the trumpet kind, thought by some to be the ancient sackbut, consisting of a tube in three parts, bent twice upon itself and ending in a bell. The middle part, bent double, slips into the outer parts, as in a telescope, so that by change of the vibrating length any tone within the compass of the instrument (which may be bass or tenor or alto or even, in rare instances, soprano) is commanded. It is the only member of the family of wind instruments whose scale, both diatonic and chromatic, is complete without the aid of keys or pistons, and which can slide from note to note as smoothly as the human voice or a violin. Softly blown, it has a rich and mellow sound, which becomes harsh and blatant when the tones are forced; used with discretion, its effect is often solemn and majestic.
2. n. (Zoöl.) The common European bittern.

WordNet 3.0

1. n. a brass instrument consisting of a long tube whose length can be varied by a U-shaped slide