A brass wind instrument, like a bass trumpet, so contrived that it can be lengthened or shortened according to the tone required; -- said to be the same as the trombone.

a medieval musical instrument resembling a trombone

the predecessor to the trombone

Early brass instrument, ancestor of the trombone.

The Sackbut (var. Sacbutt; Sackbutt; Sagbutt;), a brass instrument from the Renaissance and Baroque Eras, is an ancestor of the modern trombone. The name is derived from the Middle French sacquer and bouter ("push" and "pull") and the term survives in numerous English spelling variations including sacbut, sagbut, shagbolt and shakbusshe.