c.1300, "ability; ability to act or do; strength, vigor, might," especially in battle; "efficacy; control, mastery, lordship, dominion; 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, from Latin potis "powerful" (see potent).
Meaning "one who has power" is late 14c. Meaning "specific ability or capacity" is from early 15c. Meaning "a state or nation with regard to international authority or influence" [OED] is from 1726. Used for "a large number of" from 1660s. Meaning "energy available for work is from 1727. Sense of "electrical supply" is from 1896.
Phrase the powers that be is from Rom. xiii:1. As a statement wishing good luck, more power to (someone) is recorded from 1842. A power play in ice hockey so called by 1940. Power failure is from 1911; power steering from 1921.