Definitions for u-boatˈyuˌboʊt
Random House Webster's College Dictionary
a German submarine.
Origin of U-boat:
1910–15; < G U-Boot, short for Unterseeboot lit., undersea boat
submarine, pigboat, sub, U-boat(noun)
a submersible warship usually armed with torpedoes
Any German submarine of the First or Second World War, or any Austro-Hungarian submarine of the First World War.
Origin: A calque of U-Boot.