diamond

: a very hard usually colorless stone that is a form of carbon and is used especially in jewelry — often used before another noun — see color picture on this page

[count] : a shape that is formed by four equal straight lines and that has two opposite angles that are smaller than a right angle and two opposite angles that are larger than a right angle — compare square

a  [count] : a playing card that is marked with a red diamond shape — see picture at playing card

b  diamonds [plural] : the suit in a deck of playing cards that is marked by red diamond shapes — compare club, heart, spade

a  : the part of a baseball field that includes the area within and around the three bases and home plate : infield

b  : the entire playing field in baseball

: of or relating to the 60th or 75th anniversary of an important event (such as a marriage)

◊ It is more common for diamond to refer to the 60th anniversary of something.

— compare golden, silver