\Sack"but\, n. [F. saquebute, OF. saqueboute a sackbut,
earlier, a sort of hook attached to the end of a lance used
by foot soldiers to unhorse cavalrymen; prop. meaning, pull
and push; fr. saquier, sachier, to pull, draw (perhaps
originally, to put into a bag or take out from a bag; see
{Sack} a bag) + bouter to push (see {Butt} to thrust). The
name was given to the musical instrument from its being
lengthened and shortened.] (Mus.)
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. [Written
also {sagbut}.] --Moore (Encyc. of Music).

Note: The sackbut of the Scriptures is supposed to have been
      a stringed instrument.