mid-14c., diamaunt, diamond, "extremely hard and refractive precious stone made of pure or nearly pure carbon," from Old French diamant, from Medieval Latin diamantem (nominative diamas), from Vulgar Latin *adiamantem (which was subsequently altered by influence of the many Greek words in dia-), from Latin adamantem (nominative adamans) "the hardest metal," later, "diamond," from Greek adamas (genitive adamantos), name of a hypothetical hardest material, noun use of an adjective meaning "unbreakable, inflexible," a word of uncertain origin (see adamant (n.)).
From early 15c. as "person of great worth" (a sense also in Latin). From late 15c. as "geometric figure of four equal straight lines forming two acute and two obtuse angles." From 1590s as "playing-card stamped with one or more red diamonds." In baseball, "square space enclosed within the four bases," is American English, by 1875. As an adjective "resembling, consisting of, or set with diamonds," from 1550s.
"powdered glass or crystal," by 1904, from French diamanté, past participle of diamanter "to set with diamonds," from Old French diamant (see diamond). Diamante also was a Middle English form of diamond.
It is perhaps literally "invincible, indomitable," from a- "not" (see a- (3)) + daman "to conquer, to tame," from PIE root *deme- "to constrain, force, break (horses)" (see tame (adj.)). "But semantically, the etymology is rather strange," according to Beekes, who suggests it might be a foreign word altered in Greek by folk etymology, and compares Akkadian (Semitic) adamu.
Applied in antiquity to a metal resembling gold (Plato), white sapphire (Pliny), magnet (Ovid, perhaps through confusion with Latin adamare "to love passionately"), steel, emery stone, and especially diamond, which is a variant of this word. "The name has thus always been of indefinite and fluctuating sense" [Century Dictionary].
c. 1200, "broken ground, a rough surface," from rough (adj.). From 1640s as "the disagreeable side of anything." The meaning "a rowdy" is attested by 1837, but Century Dictionary calls this perhaps rather an abbreviation of ruffian conformed in spelling to rough. The specific sense in golf, in reference to the ground at the edge of the greens, is by 1901.
Phrase in the rough "in an unfinished or unprocessed condition" (of timber, etc.) is from 1620s, in rough diamond "diamond in its natural state," which was used figuratively, of persons, by 1700, hence diamond in the rough (by 1874 of persons, in the figurative sense "one whose good character is somewhat masked by rough manners and want of education or style").
measure of quality of a diamond, c. 1600, from water (n.1), perhaps as a translation of Arabic ma' "water," which also is used in the sense "luster, splendor."
town in northeastern India, from Tibetan dojeling "diamond island," in reference to Vajrayana (literally "vehicle of the diamond") Buddhism. The "island" being the high ground of the place's site. As a type of tea, by 1862.
The first trial of the tea plant at Darjeeling was made in 1841, with a few seeds grown in Kumaon from China stock. It was quite successful as to its growth, and the quality was approved of by the Assam tea planter who visited Darjeeling in 1846, and made the first tea here. The original plants are now to be seen. All are of gigantic size; one is a bush 50 feet in circumference and 20 feet high. [list of contributions from British India at the New Zealand Exhibition of 1865]
