D is for Dreadnought
Sounds like a great name for a steampunk superhero, but actually the name of a Royal Navy battleship. In fact, there have been Dreadnoughts in the British Royal Navy since 1553 but "the" Dreadnought was launched in 1906.
This ship's radical design (its heavy guns and the steam turbines driving it) proved to be such a success that its name came to be used for an entire generation of battleships. And from there, the word came to mean anyone or anything fearless and unstoppable.
The word crops up quite frequently in SF - e.g. as the name of ships in both Star Trek and Farscape.
Archaeopteryx Blunderbuss Chthonic Dreadnought