n (context|manufacturing) A vessel containing pressurized hot water ready for release as steam.
n (context|engineering|hydraulics) A container which stores hydraulic power for release, in the form of a pressurized fluid (often suspended within a larger tank of fluid under pressure).
n (context|computer science) A register in a calculator or computer used for holding the intermediate results of a computation or datatransfer.
n (context|finance) A derivative contract under which the seller commits to sell shares of an underlying security at a certain strike price, which the buyer is obligated to buy.