- (uncountable) Diamond is a very hard mineral made from carbon that is shiny like glass.
- The blades of cutting tools like saws and knives are sometimes coated in diamond.
- (countable) A diamond is a precious gemstone made from the mineral diamond.
- The diamond is the birthstone of April.
- (countable), (geometry) In geometry, a diamond is a rhombus shape, especially one that is taller than it is wide; ◊.
- (plural) In card games, the diamonds are one of the four playing card suits.
- The diamonds and the hearts are the two red-colored suits.
- (countable) In cards games, a diamond is a card of the diamond suit.
- I have three diamonds in my hand.