The trombone's Renaissance ancestor went by many names. Sackbut. Sagbutt. Shagbolt. Sacabuche in Spanish. Trombone itself didn't settle into common use until the seventeenth century, and even then the older names hung around in various corners of Europe like uninvited guests who couldn't quite be persuaded to leave.
Nobody agrees on where any of these words came from. The most popular theory for sackbut traces it to the Old French saquer (to pull) and bouter (to push) — a tidy description of a slide instrument, if a bit on-the-nose. But the etymology is contested, and the variant shagbolt is mysterious enough that the Oxford English Dictionary essentially throws up its hands: "origin unknown."
Early English name for trombone. Origin of name unknown (sometimes occurs as shagbolt).
I find this oddly comforting. The instrument has been around for six hundred years, has appeared in Renaissance court music, Baroque church cantatas, nineteenth-century opera orchestras, twentieth-century jazz bands, and twenty-first-century community bands in Roanoke, Virginia — and we still can't agree on what to call it or why.
There's something fitting about naming a website after the mystery. Low brass players learn early that their instrument occupies an ambiguous space: too loud for chamber music, too soft for brass bands, too serious for pop, too rowdy for the string section's taste. You get comfortable with not quite fitting in. The name shagbolt — odd, angular, origin unknown — seems about right.