Bootless once meant useless but now it most obviously means without boots. However, its roots are still visible in the expression “to boot,” meaning something extra.
Breech once meant buttocks and has retained a related meaning in the plural — breeches, or pants — and in the expressions “breech presentation” or “breech birth,” as in buttocks first. The rear end of a firearm is also known as the breech.
A caboose originally was a kitchen on a ship’s deck, but it came to mean a railroad car that provides shelter for the crew. The earliest known printed use of caboose in the latter sense was in 1859 in a lawsuit filed against the New York and Harlem Railway.
In the 17th century, a cadet was a younger son. The older son inherited the estate, and the younger one went into the army, and so today a cadet is a student at a military school. Caddie, as in the person who carries your golf clubs, has related roots.
Carbon copy originally meant a duplicate of typed or written material made by carbon paper — but nobody does that anymore. Typewriters gave way to word processors, which gave way to personal computers and printers. Still, carbon copy is sometimes used to mean an exact replica, and the abbreviation CC is used in email.