Ultra vires
A latinism meaning beyond its powers, which crops up usually in the context of a corporation or governmental authority exceeding the powers and objects as set out in its memorandum and articles of association or charter. Also of some relevance also to a Trust.
In that most valuable and intellectually rewarding pastime of checking a combatant's capacity and authority, ultra vires is the principle concern should it not have the capacity to transact in your chose kind of derivative. These days it is a rather old fashioned notion as far as a corporation goes - in most sensible jurisdicitons it has been partly or entirely ruled out by legislation, but it is liable to induce butterflies if one is dealing with a local authority.
Don't mention
derivatives and Orange County or Hammersmith and Fulham.