Etymology
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back up (v.)

1767, "stand behind and support," from back (v.) + up (adv.). The meaning "move or force backward" is by 1834. Of water prevented from flowing, by 1837.

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back off (v.)

"retreat, stop annoying someone," by 1938, from the verbal phrase, from back (v.) + off (adv.).

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get back (v.)

c. 1600 (intransitive) "to return;" 1808 (transitive) "to recover (something);" from get (v.) + back.(adv.). Meaning "retaliate" is attested by 1888.

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back seat (n.)

also back-seat, 1832, originally of coaches, from back (adj.) + seat (n.). Used figuratively for "less or least prominent position" by 1868. Back-seat driver "passenger who gives the driver unwanted advice" is attested by 1923.

You know him. The one who sits on the back seat and tells the driver what to do. He issues a lot of instructions, gives advice, offers no end of criticism and doesn't do a bit of work. ["The Back Seat Driver," Wisconsin Congregational Church Life, May 1923]
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back down (v.)

in figurative sense of "withdraw a charge," 1859, American English, from the notion of descending a ladder, etc. (such a literal sense is attested by 1849); from back (v.) + down (adv.).

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grow up (v.)

"advance toward maturity," 1530s, from grow (v.) + up (adv.). As a command to be sensible, from 1951.

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hang up (v.)

c. 1300, "suspend (something) so that it is supported only from above;" see hang (v.) + up (adv.); telephone sense by 1911. The noun hang-up "psychological fixation" is first attested 1959, from notion of being suspended in one place.

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shut up (v.)

c. 1400, "keep from view or use, render inaccessible" early 15c., "to lock up, confine," from shut (v.) + up (adv.). The meaning "cause to stop talking" is from 1814 (Jane Austen). The intransitive meaning "cease from speaking" is from 1840, also as a command to be silent, sometimes colloquialized in print as shuddup (1940). Put up or shut up "defend yourself or be silent" is U.S. slang, by 1868.

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show up (v.)

verbal phrase, by 1826 as "to disgrace through exposure;" see show (v.) + up (adv.). The meaning "to put in an appearance, be (merely) present" is by 1888. The noun sense of "an exposure of something concealed" is by 1830, colloquial.

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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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