1921; see jazz (n.); popularized 1922 in writings of F. Scott Fitzgerald; usually regarded as the years between the end of World War I (1918) and the Stock Market crash of 1929.

We are living in a jazz age of super-accentuated rhythm in all things; in a rhythm that (to "jazz" a word) is super-normal, a rhythm which is the back-flare from the rhythm of a super war. ["Jacobs' Band Monthly," Jan. 1921]

1971, in reference to a modern spiritual movement, from new + age (n.). It had been used at various times at least since the 1840s.

1855, from ice (n.) + age (n.). Perhaps translating German Eiszeit (1837). An earlier term in the same sense was glacial epoch (1841). Local scientific men had noticed from the late 18c. evidence that the Alpine glaciers once had been much larger; in the 1830s stray boulders, moraines, and polished bedrock in northern Europe (formerly interpreted as relics of catastrophic floods) began to be understood as revealing the former presence of a large ice cap there. When Agassiz, a convert to the theory, came to America in 1846 he found similar evidence in New England. The glacial theory and the notion that there had been several worldwide ice ages seems to have been generally accepted by the 1870s.

1590s, originally, as in Greek and Roman mythology, the last and worst age of the world; the archaeological sense of "period in which humans used iron tools and weapons" is from 1866 (earlier in this sense iron period, 1847).

"period between youth and old age," formerly generally understood as 40 to 50, late 14c., from middle (adj.) + age (n.). The adjective middle-aged "having lived to the middle of the ordinary human lifespan, neither old nor young" is by c. 1600.

1941, literally "daughter of command;" a Jewish girl who has reached age 12, the age of religious majority. Extended to the ceremony held on occasion of this.

1610s, "of full legal age and capacity," in ancient Rome, "of the status of one not subject to the patria potestas." For first element, see sui generis; for second element, see jurist.

"period between ancient and modern times" (formerly roughly 500-1500 C.E., now more usually 1000-1500), attested from 1610s, translating Latin medium aevum (compare German mittelalter, French moyen âge).

"temporary marked increase in the birth rate," coined 1941 from baby (n.) + boom (n.2); derivative baby-boomer (member of the one that began in the U.S. in 1945) is recorded by 1963 (in newspaper articles when they began to approach college age); earlier it had sometimes meant "a young kangaroo."

1890, from French fin de siècle "end of century," phrase used as an adjective. At the time it meant "modern;" now it means "from the 1890s." "App. first in title of a comedy, Paris fin de siècle, produced at the Gymnase, Feb. 1890" [Weekley]. French siècle "century, age" is from Latin saeculum "age, span of time, generation" (see secular).

No proof is needed of the extreme silliness of the term. Only the brain of a child or of a savage could form the clumsy idea that the century is a kind of living being, born like a beast or a man, passing through all the stages of existence, gradually ageing and declining after blooming childhood, joyous youth, and vigorous maturity, to die with the expiration of the hundredth year, after being afflicted in its last decade with all the infirmities of mournful senility. [Max Nordau, "Degeneration," English translation, 1895]