Heavily armored military combat vehicles equipped with tracks and mounted guns. Also refers to large containers for storing liquids or gases.
The military vehicle sense comes from World War I British code name 'tank' used to disguise the new weapon's true purpose - officials claimed they were building water tanks. The storage container meaning is older, from Indian 'tankh' meaning reservoir.
The word 'tank' for military vehicles was one of history's most successful code names. British engineers deliberately chose a mundane word to hide their revolutionary weapon development, and the name stuck permanently, showing how wartime secrecy can shape language.
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