A treasury is either

A government department related to finance, taxation, accountancy, and judicial responsibilities relating to revenue; i.e. a exchequer, a finance ministry or a department of the treasury.
A place or location where treasure, such as currency or precious items are kept. These can be state or royal property, church valuables or in private ownership.The head of a treasury is typically known as a treasurer. This position may not necessarily have the final control over the actions of the treasury, particularly if they are not an elected representative.
The adjective for a treasury is normally treasurial. The adjective "tresorial" can also be used, but this normally means pertaining to a treasurer.