The Renaissance ancestor of the trombone was an instrument called the sacbut. At least, sometimes it was called the sacbut. That being before the era of standardize spelling, it's also known as the sackbut, saqueboute, shakbusshes, seykebuds, sakbuds, shakebuttes, shagbutts, or shagbolts. Probably sacbut, from roots meaning "push-pull" is closest to the way it was pronounced, but who knows for sure.

The sacbut was in use by 1500, and came in four sizes (alto, tenor, bass and great bass). Professional sacbut players could execute very complex music; this was an instrument of the dance rather than the marching band. In fact, sacbuts were favored for church music because they produce a warm, almost human voice, sound.

Overall the sacbut is slightly simpler and has a smaller bore and bell than the modern tenor trombone, but if you see a picture of one it's clearly related.¹