early 14c. as a verbal phrase, "lift and take with the fingers," from pick (v.) + up (adv.). From 1510s as "take or get casually, obtain or procure as opportunity offers." Meaning "take (a person found or overtaken) into a vehicle or vessel," is from 1690s, also, of persons, "make acquaintance or take along" (especially for sexual purposes). Intransitive meaning "improve gradually, reacquire vigor or strength" is by 1741. Sense of "tidy up" is from 1861; that of "arrest" is from 1871; meaning "gain speed" is from 1922; meaning "to pay" (a check, tab, etc.) is from 1945. Pick-me-up "stimulating alcoholic drink" is attested from 1867.
"multi-vehicle crash," 1929, from verbal phrase pile up "to heap up" (c. 1400), which is attested from 1849 as "to accumulate," 1899 as "to wreck in a heap" (see pile (v.)).
command to a horse to go, 1909, probably an extended form of earlier giddap (1867), itself probably from get up. Compare gee.
The terms used to start horses in harness and to urge them to a better appreciation of the value of time comprise vulgar corruptions of ordinary speech and peculiar inarticulate sounds. Throughout England and the United States drivers start their horses by picking up the reins, drawing them gently against the animals' mouths, and exclaiming go 'long and get up; the latter appears in the forms get ap (a as in hat), giddap, and gee-hup or gee-up. [H. Carrington Bolton, "Talking to Domestic Animals," in The American Anthropologist, March 1897]