1. A large container for storing liquids or gases: There were several tanks filled with water and fish.
2. The amount of liquid or gas that a tank holds: Gary bought a tank of gas at a much higher price.
3. A sturdy container with rectangular glass sides, in which to keep live fish: Gary had two tanks in his living room for his tropical fish.
4. A fairly small body of water, especially one used for water storage: The tank was equipped with a filter to ensure that the water was drinkable.
5. A large armored combat vehicle with treads, a rotating turret, and a heavy gun used by military organizations: Someone has suggested that the best place for a military tank is in a museum.
6. In the U.S., an informal statement referring to a very bad situation or condition: Right now the global economy is in the tank.
7. A lightproof container for developing film, designed so that processing chemicals can be poured in and out without letting light get in: The camera technologist used a tank for transporting the solutions used for developing films.

1. To completely fail or to suffer a sudden decline or failure: Today several trading stocks tanked.

The movie tanked over the weekend even though it was supposed to be so great.

2. To make no effort to win a contest or to deliberately lose a game, match, etc.; such as, a tennis match, a basketball game, a football game, etc.: There are those who say the team deliberately tanked the game.

An organization which is made up of a group of people who reflect on and envisage new ideas for a particular subject or who give advice about what should be done in certain situations: The professor was asked to join the think tank so he could help the group come up with a solution to improve the deteriorating educational system.