die2
• noun 1 singular form of DICE. 2 (pl. dies) a device for cutting or moulding metal or for stamping a design onto coins or medals.
— PHRASES the die is cast an event has happened that cannot be changed. (as) straight as a die 1 completely straight. 2 entirely open and honest.
— USAGE In modern English the singular die (rather than dice) for sense 1 is now uncommon. Dice is widely used for both the singular and the plural.
— ORIGIN Old French de, from Latin datum ‘something given or played’.
http://www.askoxford.com/concise_oed/die_2?view=ukdice
• noun (pl. same; sing. also die) a small cube with faces bearing from one to six spots, used in games of chance. See also DIE2.
• verb cut (food) into small cubes.
— PHRASES dice with death take serious risks. no dice informal, chiefly N. Amer. used to indicate an unsuccessful attempt or request.
— USAGE Historically, dice is the plural of die, but in modern standard English dice is used as both the singular and the plural.
— ORIGIN Old French des, plural of de, from Latin datum ‘something given or played’.
http://www.askoxford.com/concise_oed/dice?view=ukDice is both singular and plural - at least in BE. But, a dice is never cast and a die is usually not thrown. As LEO does not suggest the phrase "to cast the dice" I cannot see where LEO is wrong.