"that roars or bellows; making or characterized by noise or disturbance," late 14c., present-participle adjective from roar (v.). Used of periods of years characterized by noisy revelry, especially roaring twenties (1930, which OED credits to "postwar buoyancy"); but also, in Australia, roaring fifties (1892, in reference to the New South Wales gold rush of 1851). Roaring Forties in reference to exceptionally rough seas between latitudes 40 and 50 south, is attested from 1841.

The "roaring fifties" are still remembered as the days when Australia held a prosperity never equalled in the world's history and a touch of romance as well. The gold fever never passed away from the land. [E.C. Buley, "Australian Life in Town and Country," 1905]

Roaring boys, roaring lads, swaggerers : ruffians : slang names applied, about the beginning of the seventeenth century, to the noisy, riotous roisterers who infested the taverns and the streets of London, and, in general, acted the part of the Mohocks of a century later. Roaring girls are also alluded to by the old dramatists, though much less frequently. [Century Dictionary]

This is from the use of roar (v.) in old London slang for "behave in a riotous and bullying manner" (1580s).

Middle English roren, "shout out, cry out with a full, loud, continued sound," from Old English rarian "roar, wail, lament, bellow, cry," probably of imitative origin (compare Middle Dutch reeren, German röhren "to roar;" Sanskrit ragati "barks;" Lithuanian rieju, rieti "to scold;" Old Church Slavonic revo "I roar;" Latin raucus "hoarse," all alike probably imitative).

Of animals, the wind, etc., early 14c. Sense of "laugh loudly and continuously" is by 1815. The meaning "travel in a motor vehicle making a loud noise" is by 1923. Related: Roared; roaring.

abbreviation of Metro Goldwyn-Mayer, U.S. movie studio noted for the roaring lion in its emblem, attested from 1933.

c. 1600, "rapid stream," from French torrent (16c.) and directly from Latin torrentem (nominative torrens) "rushing, roaring" (of streams), also "a rushing stream," originally as an adjective "roaring, boiling, burning, parching, hot, inflamed," present participle of torrere "to parch" (from PIE root *ters- "to dry"). The extension to any onrush (of words, feelings, etc.) first recorded 1640s.

"loud noise of some duration, a resonant sound long continued," Old English dyne (n.), related to dynian (v.), from Proto-Germanic *duniz (source also of Old Norse dynr, Danish don, Middle Low German don "noise"), from PIE root *dwen- "to make noise" (source also of Sanskrit dhuni "roaring, a torrent").

also rip-roaring, "full of vigour, spirit, or excellence" [OED], 1834, in affectations of Western U.S. (Kentucky) slang, altered from riproarious "boisterous, violent" (1821), from rip (v.) "tear apart" + uproarious; see uproar. Rip-roarer was noted as a nickname for a Kentuckian in 1837. Related: Riproaringest.

late 14c., "roaring, shouting;" 1590s, "wailing, weeping," present-participle adjective from cry (v.). Sense of "demanding attention or remedy" is from c. 1600. U.S. colloquial expression of disgust, impatience, etc., for crying out loud, is by 1921, probably a euphemism for for Christ's sake.

"a deep, heavy, continuous rattling or dully roaring sound," as of thunder, late 14c., from rumble (v.). From 14c. to 17c. it also meant "confusion, disorder, tumult." The slang noun meaning "gang fight" is by 1946. The meaning "backmost part of a carriage" (typically reserved for servants or luggage) is from 1808 (earlier rumbler, 1801), probably from the effect of sitting over the wheels; hence rumble seat (1828), later transferred to automobiles.

"periodically recurring sexual excitement in animals; animal mating season" (originally of deer), early 15c., from Old French rut, ruit, from Late Latin rugitum (nominative rugitus) "a bellowing, a roaring," from past participle of Latin rugire "to bellow" (from PIE imitative root *reu-). If so, the notion is of the noise made by deer at the time of sexual excitement. The noun rut "roar of the sea" (1630s) in Scottish and persisting in New England dialect is of uncertain connection.

1843 as the years of someone's life between 40 and 49; from 1840 as the fifth decade of years in a given century. See forty. Also a designation applied in various places and times to certain oligarchies, ruling classes, or governing bodies.

It is well known that society in the island [Guernsey] is, or perhaps we ought to say, for many years was, divided into two sets, called respectively the Sixties and the Forties, the former composed of the old families and those allied to them, the latter of families of newly-acquired wealth and position. [The Dublin Review, October 1877]

Roaring Forties are rough parts of the ocean between 40 and 50 degrees latitude.