Longman Dictionary of Contemporary English - diamond

~ n 1 »STONE« a very hard valuable stone, that usually has no colour and is used in jewellery  (Did you see the size of that diamond engagement ring?) 2 »SHAPE« a shape with four straight sides of equal length that stands on one of its points 3 »ON A PLAYING CARD« a) a diamond shape printed in red on a playing card b) one of the cards in the set that are printed in this way  (the queen of diamonds) 4 »SPORTS FIELD« a) the area in a baseball field within the diamond shape formed by the four bases (base1 (8)) b) the whole playing field used in baseball