tank1 S2 W2 [countable]
a large container for storing liquid or gas:
The water tank is leaking.
Somehow the chemical got from a storage tank into water supplies.
fish/marine/breeding tank (=for keeping or breeding fish in)
the plane's fuel tank
2 also tankful
the amount of liquid or gas held in a tank:
We set off next day on a full tank.
a tankful of petrol
a heavy military vehicle that has a large gun and runs on two metal belts fitted over its wheels
a large artificial pool for storing water
5 American English informal
failing and losing money
be/go in the tank
Sales can't keep going up, but that doesn't mean the industry is going in the tank.