I. e., the thing you stick in the bell of your horn to change the sound and/or make it softer. Could be anything. I'll do a quick recap here and get into it more next time.
The trumpet in its present state is a relatively new phenomenon-final evolution in the mid-1800's. It's a good bet that early on, the complaints of neighbors got some horn players to jam a rag into their bells to keep peace in the 'hood. Of course, there was sometimes a quiet woodshed to go to, but the idea of sticking something in the end of the horn to alter the sound didn't pick up steam until some time later.
As far as I know, there is no notation in a classical score asking for a mute (fancy Italian word: sordina) until well into the 20th century. After all, you choose to write for a trumpet because the thing is so damned loud. Likewise, no mutes in Sousa, or James Reese Europe.
