c. 1300, seculer, in reference to clergy, "living in the world, not belonging to a religious order," also generally, "belonging to the state" (as opposed to the Church), from Old French seculer, seculare (Modern French séculier) and directly from Late Latin saecularis "worldly, secular, pertaining to a generation or age," in classical Latin "of or belonging to an age, occurring once in an age," from saeculum "age, span of time, lifetime, generation, breed."
This is from Proto-Italic *sai-tlo-, which, according to Watkins, is PIE instrumental element *-tlo- + *sai- "to bind, tie" (see sinew), extended metaphorically to successive human generations as links in the chain of life. De Vaan also connects it with "bind" words and lists as a cognate Welsh hoedl "lifespan, age." An older theory connected it to words for "seed," from PIE root *se- "to sow" (see sow (v.), and compare Gothic mana-seþs "mankind, world," literally "seed of men").
The ancient Roman ludi saeculares was a three-day, day-and-night celebration coming once in an "age" (120 years). Ecclesiastical writers in Latin used it as those in Greek did aiōn "of this world" (see cosmos). It is the source of French siècle "century." The meaning "of or belonging to an age or a long period," especially occurring once in a century, was in English from 1590s.
From mid-14c. in the general sense of "of or belonging to the world, concerned in earthly more than in spiritual, life;" also of literature, music, etc., "not overtly religious." In English, in reference to humanism and the exclusion of belief in God from matters of ethics and morality, from 1850s. Related: Secularly.
"exclusive attention to the present life and its duties; doctrine that morality should be based on the well-being of man in the present life, without regard to religious belief or a hereafter," 1843, from secular + -ism.
Secularity (late 14c., seculerte ) was used for "civil or temporal power, the business of layman life; quality or condition of being secular" (from Old French secularite and Medieval Latin sæcularitas).
1530s, "one hundred" (of anything), from Latin centuria "group of one hundred" of things of one kind (including a measure of land and a division of the Roman army, one-sixteenth of a legion, headed by a centurion), from centum "hundred" (see hundred) on analogy of decuria "a company of ten."
Used in Middle English from late 14c. as a division of land, from Roman use. The Modern English meaning "period of 100 years," reckoned from any starting point, is attested from 1650s, short for century of years (1620s). Latin centuria was not used in the sense "one hundred years," for which saeculum was the word (see secular). The older, general sense is preserved in the meaning "score of 100 points" in cricket and some other sports. The century-plant (American aloe), 1843, was believed to bloom only after a century of growth.
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]
c. 1300, "secular tribunal," from Old North French consistorie (Old French consistoire, 12c.) and directly from Late Latin consistorium "waiting room, meeting place of the imperial council," from Latin consistere (see consist). Meaning "Church council, an ecclesiastical court" is from early 14c. Related: Consistorial.