diamond in the rough, a

An individual of intrinsic merit but uncultivated manners. The simile comes from mining, where the uncut, unpolished dia- mond resembles a hunk of worthless rock but may, after processing, be both beautiful and very valuable. John Fletcher’s 1624 play, AWife for a Month, has it, “She is very honest, and will be hard to cut as a rough diamond” (4.2).