Etymology
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up-river (prep.)
1773, from up + river. As an adverb from 1848.
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up-to-date (adv.)
1840, "right to the present time," from phrase up to date, probably originally from bookkeeping. As an adjective from 1865. Meaning "having the latest facts" is recorded from 1889; that of "having current styles and tastes" is from 1891.
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back up (v.)
1767, "stand behind and support," from back (v.) + up (adv.). Meaning "move or force backward" is by 1834. Of water prevented from flowing, by 1837.
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build-up (n.)
also buildup, 1927, "accumulation of positive publicity." Of any accumulation (but especially military) from 1943. The verbal phrase is attested from late 14c.; see build (v.) + up (adv.).
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mock-up (n.)

also mockup, "model, simulation" 1919, perhaps World War I, from the verbal phrase mock up "make an experimental model" (1911), from mock (v.) + up (adv.).

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follow-up (n.)
1905, originally in the argot of sales and business, from verbal phrase follow up "pursue closely, act on energetically" (1794); see follow (v.) + up (adv.).
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start-up (n.)
also startup, 1550s, "upstart," from verbal phrase (attested from c. 1200 in sense "rise up;" 1590s as "come suddenly into being"); see start (v.) + up (adv.). Meaning "action of starting up" is from 1845. See start (v.) + up (adv.).
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sun-up (n.)
also sunup, "sunrise," 1712, from sun (n.) + up (adv.). In local use in U.S., and, according to OED, also in Caribbean English and formerly in South Africa.
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pin-up (adj.)

1670s, of clothing, "adapted for being pinned up," from the verbal phrase (attested from mid-15c. in the sense "affix in a prominent place"), from pin (v.) + up (adv.). From 1940, in reference to pictures of "winsome young ladies in daring undress" ("Life," May 6, 1940) such as soldiers pinned up on their dugout walls, etc. The thing itself is older than the name. The noun in this sense is recorded from 1943.

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mix-up (n.)

"state of confusion," 1841, from the colloquial verbal phrase mix up "to confuse, entangle mentally" (1806), from mix (v.) + up (adv.). Of fighters, to mix it up "exchange blows" is by 1898.

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