jubilee (n.)
late 14c., in the Old Testament sense, from Old French jubileu "jubilee; anniversary; rejoicing" (14c., Modern French jubilé), from Late Latin iubilaeus "the jubilee year," originally an adjective, "of the jubilee," from Greek iabelaios, from iobelos, from Hebrew yobhel "jubilee," formerly "a trumpet, ram's horn," literally "ram." The original jubilee was a year of emancipation of slaves and restoration of lands, to be celebrated every 50th year (Levit. xxv:9); it was proclaimed by the sounding of a ram's horn on the Day of Atonement.

The form of the word was altered in Latin by association with unrelated Latin iubilare "to shout with joy" (for which see jubilant), and the confusion of senses has continued in the Romanic languages and English. The general sense of "season of rejoicing" is first recorded mid-15c. in English, however through early 20c. the word kept its specific association with 50th anniversaries. As a type of African-American folk song, it is attested from 1872. The Catholic Church sense of "a period for remission of sin penalties in exchange for pilgrimages, alms, etc." was begun in 1300 by Boniface VIII.