late 13c., "younger, not as old as another," from Latin iunior "younger, more young," comparative of iuvenis "young; a young man," etymologically "one who possesses vital force," from PIE root *yeu- "vital force, youthful vigor" (see young (adj.)). Used after a person's name to mean "the younger of two" from late 13c. Abbreviation Jr. is attested from 1620s. Meaning "of lesser standing, more recent" is from 1766. That of "meant for younger people, of smaller size" is from 1860. Junior miss "young teenage girl" is from 1907. In U.S. colleges, "pertaining to the third-year." Junior college first attested 1896; junior high school is from 1909.

The junior high school is rapidly becoming the people's high school. The percentage of pupils completing the ninth year is constantly rising where junior high schools have been established. [Anne Laura McGregor, "Supervised Study in English for Junior High School Grades," New York, 1921]

coniferous evergreen shrub of northern regions, late 14c., gynypre, etc. (later altered to conform to Latin), from Latin iuniperus "the juniper tree" (source of Old French genevre, French genièvre, Spanish enebro, Portuguese zimbro, Italian ginepro, and, via Old French, Middle Dutch genever), a word of uncertain origin.

Perhaps it is related to iunco "reed," but there are phonetic difficulties. Watkins has it from PIE *yoini-paros "bearing juniper berries," from *yoi-ni- "juniper berry," perhaps from a non-IE language, + *-paro "producing" (from PIE root *pere- (1) "to produce, procure"). Applied to various North American species from 1748. In the English Bible (late 14c.), it renders Hebrew rethem, the name of a white-flowered shrub unrelated to the European evergreen, as the Latin word does in the Vulgate.

mid-14c., junke "old cable or rope," cut in bits and used for caulking, etc., a nautical word of uncertain origin, perhaps from Old French junc "rush, reed," also used figuratively as a type of something of little value, from Latin iuncus "rush, reed" (but OED finds "no evidence of connexion").

It was extended to "old refuse from boats and ships" (1660s), then to "old or discarded articles of any kind" (1884), usually with a suggestion of reusability. Meaning "salt meat used on long voyages" is from 1762. Meaning "narcotic drug" is from 1925. Junk food is from 1971; junk art is from 1961; junk mail first attested 1954; junk bond from 1979.