Etymology
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ultra vires 

Latin, literally "beyond powers," from ultra "beyond" (see ultra-) + vires "strength, force, vigor, power," plural of vis (see vim). Usually "beyond the legal or constitutional power of a court, etc."

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beef up (v.)

"add strength," 1941, from college slang, from beef (n.) in slang sense of "muscle-power" (1851).

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non compos mentis 

c. 1600, in law, "not capable, mentally, of managing one's own affairs," Latin, "not master of one's mind," from non "not" + compos "having power" (from com- "together" + potis "powerful") + mentis "of the mind," genitive of mens "mind."

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aqua fortis (n.)

also aquafortis, old commercial name for "diluted nitric acid," c. 1600, Latin, literally "strong water;" for the elements, see aqua- + fort. Also see aqua. So called for its power of dissolving metals (copper, silver) which are unaffected by other agents.

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attention deficit disorder (n.)

(abbreviated ADD), introduced as a diagnosis in the third edition of the "Diagnostic and Statistical Manual of Mental Disorders" (1980), from attention in the "power of mental concentration" sense. Expanded to attention deficit hyperactivity disorder ("the co-existence of attentional problems and hyperactivity, with each behavior occurring infrequently alone;" ADHD) in DSM-III (1987).

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common sense (n.)

late 14c., originally an internal mental power supposed to unite (reduce to a common perception) the impressions conveyed by the five physical senses (Latin sensus communis, Greek koine aisthesis). Thus "ordinary understanding, without which one is foolish or insane" (1530s); the meaning "good sense" is from 1726. Also, as an adjective, common-sense "characterized by common sense" (1854).

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carte blanche (n.)

1707, "paper duly authenticated by a signature and otherwise blank, left to someone to be filled in at his discretion," French, literally "white paper," from carte (see card (n.1)) + blanche, from Old French blanc "white," a word of Germanic origin (see blank (adj.)). The figurative sense of "full discretionary power, unrestricted permission or authority in some manner" is from 1766. Compare the native blank check, used in the same figurative sense.

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hands down (adv.)

to win something hands down (1855) is from horse racing, from a jockey's gesture of letting the reins go loose in an easy victory.

The Two Thousand Guinea Stakes was not the best contested one that it has been our fortune to assist at. ... [T]hey were won by Meteor, with Scott for his rider; who went by the post with his hands down, the easiest of all easy half-lengths. Wiseacre certainly did the best in his power to spoil his position, and Misdeal was at one time a little vexatious. [The Sportsman, report from April 26, 1840]

Ancient Greek had akoniti "without a struggle, easily," from akonitos (adj.), literally "without dust," specifically "without the dust of the arena."

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jolie laide (n.)

"girl or woman whose attractiveness defies standards of beauty," 1849, a French expression (by 1780 in French), from fem. singular of joli "pretty" (see jolly) + laid "ugly," from Frankish *laid (see loath (adj.)).

Of beauty, as we narrowly understand it in England, [the 18c. French woman of society] had but little; but she possessed so many other witcheries that her habitual want of features and complexion ceased to count against her. Expression redeemed the absence of prettiness and the designation jolie laide was invented for her in order to express her power of pleasing despite her ugliness. ["The Decadence of French Women," Blackwood's Edinburgh Magazine, October 1881]
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silver bullet (n.)

"a remedy which is very effective, almost magical;" see silver (adj.) + bullet (n.). The belief in the magical power of silver weapons to conquer foes goes back at least to ancient Greece (as in Delphic Oracle's advice to Philip of Macedon). In Britain, silver bullets as a superstitious countercharm figure in the fictitious Popish Plot (1678).

'Cause champed silver kills stone-dead
Such as are musket-proof 'gainst lead.
[Thomas Ward, from "England's Reformation," 1710]

English folklore beliefs recorded from early 19c. held that a witch could be wounded or revealed (if transformed) only by a wound from a silver bullet. Similar fancies are reported in folk-tales from Ireland and Iceland. The belief in the killing efficacy of silver bullets was transferred to vampires by 1816.

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