What is Mediate Powers?

Legal Definition
Those incident to primary powers given by a principal to his agent For example, the general authority given to collect, receive, and pay debts due by or to the principal is a primary power. In order to accomplish this, it is frequently required to settle accounts, adjust disputed claims, resist those which are unjust, and answer and defend suite. These subordinate powers are sometimes called "mediate powers." Story, Ag. ยง 58.
-- Black's Law Dictionary
Legal Definition
Powers incidental to authority granted.
-- Ballentine's Law Dictionary