The story
From semi- + dreadnought.
Etymology from Wiktionary, CC BY-SA 4.0.
Today it means: A type of advanced pre-dreadnought battleship from the very early 20th century, carrying a main armament composed entirely of big guns of different calibers (typically having four guns of the largest caliber, plus a larger number of smaller big guns). It was superior to earlier pre-dreadnoughts, but still not as powerful as the dreadnought introduced in 1906. Full definition →
From semi- + dreadnought.
Etymology from Wiktionary, CC BY-SA 4.0.