late 14c., as a type of diving bird, agent noun from dip (v.). As "a ladle or long-handled utensil for drawing liquid," from 1783, chiefly American English. Also "a Dunker, an Anabaptist" (1610s); "one who dips snuff" (1870). As the popular U.S. name for the asterism known in Britain as The Plough or Charles's Wain, attested by 1833, so called for the arrangement of the stars. Compare Big Dipper.
Sense deteriorated from "thin layer atop liquid" to "film of dirt," then just "dirt." Meaning "lowest class of humanity" is 1580s; scum of the Earth is from 1712. Adopted in Romanic (Old French escume, Modern French écume, Spanish escuma, Italian schiuma).
Meaning "action of scooping" is from 1742; that of "amount in a scoop" is from 1832. Sense of "a big haul, as if in a scoop net" is from 1893. The journalistic sense of "news published before a rival" is first recorded 1874, American English, from earlier commercial slang verbal sense of "appropriate so as to exclude competitors" (c. 1850).
Old English liccian "to pass the tongue over the surface, lap, lick up," from Proto-Germanic *likkon (source also of Old Saxon likkon, Dutch likken, Old High German lecchon, German lecken, Gothic bi-laigon), from PIE root *leigh- "to lick."
French lécher, Italian leccare are said to be Germanic loan words. The figurative lick (one's) lips in eager anticipation is from c. 1500. Lick-ladle (1849) was an old phrase for a (human) parasite. To lick (someone or something) into shape (1610s) is in reference to the supposed ways of bears:
Beres ben brought forthe al fowle and transformyd and after that by lyckyng of the fader and the moder they ben brought in to theyr kyndely shap. ["The Pylgremage of the Sowle," 1413]