A very small "baby" submarine designed for specific localized missions, usually while tethered to a submarine or ship for life support and communications. Slang synonyms: midget-submarine, anchor.
A small nonmilitary, non-nuclear submarine for exploration.
A term used primarily by some navies for nuclear submarines, termed "true submersibles", because they cannot retroactively declare that their non-nuclear submarines should be called by a different name.
A retroactive term used for non-nuclear submarines; nuclear submarines are termed "true submarines".
Able to be submerged.
Synonym of subway: a railway that is under the ground.
A movement or organisation of people who resist artistic convention.
A movement or organisation of people who resist political convention.
Regions beneath the surface of the earth, both natural (eg. caves) and man-made (eg. mines).
Hidden, furtive, secretive.
Below the ground; below the surface of the Earth.
Outside the mainstream, especially unofficial and hidden from the authorities.
To route electricity distribution cables underground.
Below the ground.
Secretly.