A treasury is either
A government department related to finance and taxation.
A place or Schatzkammer where currency or precious items (gold, diamonds, etc.) is/are kept.
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. Wikipedia