Etymology
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buddy (n.)

1850, American English, possibly an alteration of brother, or from British colloquial butty "companion" (1802), itself perhaps a variant of booty in booty fellow "confederate who shares plunder" (1520s). But butty, meaning "work-mate," also was a localized dialect word in England and Wales, attested since 18c., and long associated with coal miners. Short form bud is attested from 1851. Reduplicated form buddy-buddy (adj.) attested by 1952, American English.

Lenny Kent, a long-time fave here, is really in his element. ... After four weeks here he's got everyone in town saying, "Hiya, Buddy, Buddy" with a drawl simulating his. [Review of Ned Schuyler's 5 O'Clock Club, Miami Beach, Fla., Billboard, Nov. 12, 1949]

Buddy system attested from 1920.

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system (n.)
1610s, "the whole creation, the universe," from Late Latin systema "an arrangement, system," from Greek systema "organized whole, a whole compounded of parts," from stem of synistanai "to place together, organize, form in order," from syn- "together" (see syn-) + root of histanai "cause to stand," from PIE root *sta- "to stand, make or be firm."

Meaning "set of correlated principles, facts, ideas, etc." first recorded 1630s. Meaning "animal body as an organized whole, sum of the vital processes in an organism" is recorded from 1680s; hence figurative phrase to get (something) out of one's system (1900). Computer sense of "group of related programs" is recorded from 1963. All systems go (1962) is from U.S. space program. The system "prevailing social order" is from 1806.
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buddy (v.)

1925, usually with up, from buddy (n.); perhaps originally U.S. underworld slang. Related: Buddied; buddying.

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Dewey Decimal system (n.)

library classification system that organizes information into 10 broad areas subdivided numerically into progressively smaller topics, by 1885, named for Melvil Dewey (1851-1931) who proposed it 1876 while acting librarian of Amherst College. He also crusaded for simplified spelling and the metric system.

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bud 
familiar form of address for a male, 1851, perhaps a shortening of buddy (q.v.) and ultimately from brother.
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bub (n.1)
also bubby, familiar address for males, 1839, perhaps a variation of bud "a little boy" (1848), American English colloquial; perhaps from German bube "boy." But sometimes, along with bud, assumed to be a corruption of brother (compare buddy, bubba).
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Beatles (n.)
seminal rock and pop group formed in Liverpool, England; named as such 1960 (after a succession of other names), supposedly by then-bassist Stuart Sutcliffe, from beetles (on model of Buddy Holly's band The Crickets) with a pun on the musical sense of beat. Their global popularity dates to 1963.
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DOS 

"computer operating system using a disk storage device," 1967, acronym of disk operating system.

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systematize (v.)
"make into a system," 1764, from French systématiser or a native formation from system (Greek stem systemat-) + -ize. Related: Systematized; systematizing.
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drainage (n.)

1650s, "act or process of draining," from drain (v.) + -age. Sense of "the water carried off by a system of rivers" is by 1860. Meaning "system by means of which something is drained" is by 1878.

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