trombone

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun 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.

from The Century Dictionary.

• noun A large musical instrument of the trumpet family.

from the GNU version of the Collaborative International Dictionary of English.

• noun (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.
• noun (Zoöl.) The common European bittern.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun 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♭).
• noun The common European bittern.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a brass instrument consisting of a long tube whose length can be varied by a U-shaped slide