early 14c., from Old French diamant, from Medieval Latin diamantem (nominative diamas), from Vulgar Latin *adiamantem (altered by influence of the many Greek words in dia-), from Latin adamantem (nominative adamans) "the hardest metal," later, "diamond" (see adamant). Playing card suit is from 1590s; Sense in baseball is American English, 1875.
Someone or something with potential or talent but lacking training or polish: “Her singing voice is beautiful, but she needs help with her gestures; she's a diamond in the rough.” This phrase refers to the fact that diamonds found in nature are rough and uneven. They must be cut and polished to bring out their true beauty.
A person of exceptional qualities or potential but lacking refinement or polish; a wonderful and surprising specimen: looked like a nerd, but rather was a diamond in the rough
(1.) A precious gem (Heb. yahalom', in allusion to its hardness), otherwise unknown, the sixth, i.e., the third in the second row, in the breastplate of the high priest, with the name of Naphtali engraven on it (Ex. 28:18; 39:11; R.V. marg., "sardonyx.") (2.) A precious stone (Heb. shamir', a sharp point) mentioned in Jer. 17:1. From its hardness it was used for cutting and perforating other minerals. It is rendered "adamant" (q.v.) in Ezek. 3:9, Zech. 7:12. It is the hardest and most valuable of precious stones.