power-broker (n.)

c. 1300, pouer, "ability; ability to act or do; strength, vigor, might," especially in battle; "efficacy; control, mastery, lordship, dominion, ability or right to command or control; legal power or authority; authorization; military force, an army," from Anglo-French pouair, Old French povoir, noun use of the infinitive, "to be able," earlier podir (9c.), from Vulgar Latin *potere (source also of Spanish poder, Italian potere), from Latin potis "powerful" (from PIE root *poti- "powerful; lord").

Whatever some hypocritical ministers of government may say about it, power is the greatest of all pleasures. It seems to me that only love can beat it, and love is a happy illness that can't be picked up as easily as a Ministry. [Stendhal "de l'Amour," 1822]

Meaning "one who has power, person in authority or exercising great influence in a community" is late 14c. Meaning "a specific ability or capacity" is from early 15c. In mechanics, "that with which work can be done," by 1727.

Sense of "property of an inanimate thing or agency of modifying other things" is by 1590s. Meaning "a state or nation with regard to international authority or influence" [OED] is from 1726. Meaning "energy available for work is from 1727. Sense of "electrical supply" is from 1896.

Colloquial a power of for "a large quantity of, a great number of" is from 1660s (compare powerful). Phrase the powers that be "the authorities concerned" is from Romans xiii.1. As a statement wishing good luck, more power to(someone) is recorded from 1842. A man-advantage power play in ice hockey so called by 1940. Power failure "failure of the (electrical) power supply" is from 1911; power steering in a motor vehicle is from 1921. Power politics "political action based on or backed by threats of force" (1937) translates German Macht-politik.

mid-14c. (mid-13c. in surnames), "commercial agent, factor," also "an agent in sordid business," from Anglo-French brocour "small trader," from abrokur "retailer of wine, tapster;" perhaps from Portuguese alborcar "barter," but more likely from Old French brocheor, from brochier "to broach, tap, pierce (a keg)," from broche (Old North French broke, broque) "pointed tool" (see broach (n.)), with an original sense of "wine dealer," hence "retailer, middleman, agent." In Middle English, used contemptuously of peddlers and pimps, "one who buys and sells public office" (late 14c. in Anglo-French), "intermediary in love or marriage" (late 14c.).