Etymology
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percentage (n.)

"a proportion or rate per hundred," 1789, from percent + -age. Commercial sense of "profit, advantage" is from 1862.

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A.P.R. 
also APR, abbreviation of annual percentage rate, attested from 1979, American English.
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contango (n.)

1853, "charge made or percentage received by a broker or seller for deferring settlement of a stock sale," a stockbroker's invention, perhaps somehow derived from continue, or from Spanish contengo "I contain, refrain, restrain, check." Continuation was used in this sense from 1813. As a verb, from 1900.

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kitty (n.2)

"pool of money in a card game," 1884, American English, of uncertain origin. OED connects it with kit (n.1) in the 19c. sense of "collection of necessary supplies;" but perhaps it is rather from northern England slang kitty "prison, jail, lock-up" (1825), a word itself of uncertain origin.

By the Widow, or as it is more commonly known as "Kitty," is meant a percentage, taken in chips at certain occasions during the game of Poker. This percentage may be put to the account of the club where the game is being played, and defrays the cost of cards, use of chips, gas, attendance, etc. The Kitty may, however, be introduced when no expenses occur. ["The Standard Hoyle," New York, 1887]
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spiffy (adj.)
1853, of uncertain origin, probably related to spiff "well-dressed man." Uncertain relationship to spiff (n.) "percentage allowed by drapers to their young men when they effect sale of old fashioned or undesirable stock" (1859), or to spiflicate "confound, overcome completely," a cant word from 1749 that was "common in the 19th century" [OED], preserved in American English and yielded slang spiflicated "drunk," first recorded in that sense 1902.
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junior (adj.)

late 13c., "younger, not as old as another," from Latin iunior "younger, more young," comparative of iuvenis "young; a young man," etymologically "one who possesses vital force" (from PIE root *yeu- "vital force, youthful vigor;" see young (adj.)).

Used after a person's name to mean "the younger of two" from late 13c. Abbreviation Jr. is attested from 1620s. Meaning "of lesser standing, more recent" is from 1766. That of "meant for younger people, of smaller size" is from 1860. Junior miss "young teenage girl" is from 1907. In U.S. colleges, "pertaining to the third-year." Junior college is attested by 1896; junior high school is from 1909.

The junior high school is rapidly becoming the people's high school. The percentage of pupils completing the ninth year is constantly rising where junior high schools have been established. [Anne Laura McGregor, "Supervised Study in English for Junior High School Grades," New York, 1921]
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commission (n.)
Origin and meaning of commission

mid-14c., "authority entrusted to someone, delegated authority or power," from Old French commission and directly from Latin commissionem (nominative commissio) "act of committing," in Medieval Latin "delegation of business," noun of action from past participle stem of committere "to unite, connect, combine; to bring together," from com "with, together" (see com-) + mittere "to release, let go; send, throw" (see mission).

Meaning "document delegating authority" is from early 15c.; meaning "body of persons charged with authority for the performance of certain special duties" is from late 15c. Sense of "anything entrusted to anyone to perform" is from 1560s; sense of "act of committing or doing" is from 1590s.

Naval sense "period of active service of a warship" is by 1882 (in commission "under the command of an officer" is from 1733). Hence out of commission "laid up in a navy yard or in reserve" (1878), subsequently extended to other machinery, and, figuratively, to persons or human qualities by 1917.

In commercial use, "authority delegated by another for the purchase and sale of goods," 1620s. Meaning "allowance made or percentage given to an agent for transacting business" is from 1725.

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