redshirt

What it means

1. historicalA supporter of the Italian nationalist leader Giuseppe Garibaldi, especially a member of his thousand-man army which conquered Sicily.First known use 19th c.

   Loyal regiments from Naples and other provinces of the mainland fought valiantly and were victorious un several skirmishes against the redshirts near Capua.

   2011, David Gilmour, The Pursuit of Italy, Penguin, published 2012, page 196

2. historicalA revolutionary or anarchist.First known use 19th c.
3. UShobbiesA college athlete who spends a year not participating in official athletic activities, but does not lose his or her eligibility to participate in following years.First known use 20th c.

In a sentence

Loyal regiments from Naples and other provinces of the mainland fought valiantly and were victorious un several skirmishes against the redshirts near Capua.

2011, David Gilmour, The Pursuit of Italy, Penguin, published 2012, page 196

Where it comes from

1. Italiancamicia rossa
2. Englishredshirt

Calque of Italian camicia rossa, equivalent to red + shirt. In later senses with reference to the uniforms or outfits worn by such people. The fandom slang sense emerged from the tendency of red-uniformed Starfleet officers to die in episodes of Star Trek: The Original Series.

First known use: 19th c.