c. 1300, "to dash, run, rush," probably from or related to Old Norse flengja "to flog," which is of uncertain origin, perhaps from Proto-Germanic *flang- (source also of Old Swedish flenga "strike," Danish flænge "slash, gash"), from a nasalized variant of PIE root *plak- (2) "to strike." Meaning "to throw, cast, hurl" is from mid-14c. An obsolete word for "streetwalker, harlot" was fling-stink (1670s). Related: Flung; flinging, but in Middle English with past tense flang, past participle flungen.
early 14c., "attempt, attack," (in phrase make a fling), from fling (v.). Hence have a fling at, etc. "make a try." From 1560s as "a wild dash, an excited kicking up." Sense of "period of indulgence on the eve of responsibilities" first attested 1827. Meaning "vigorous dance" (associated with the Scottish Highlands) is from 1804.