Sackbut n. : 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.

Example:
What is the difference between a Sackbut and a trombone?

Taxonomy
trombones, sackbut, instrument, Tenor, Nuremberg, bass, bell, cornetts, violins, trumpet, Sonata, basso continuo, music, voices, bass trombones, 17th century, pitch, SWV.

Defination from the web:
Sackbut' is often used in recent times to differentiate a historic trombone from a modern one. ... The next word to appear in the 15th century that implicated a slide was the sackbut group of words. ... These old tunings can come naturally on a sackbut. ...