dice / die
The cube you throw, singular and plural.
Die is the singular: Roll the die again. Dice is the plural: a pair of dice. A common error is to use dice as a singular, as in Pass me a dice. For a single cube, use die: Pass me a die.
Examples
UseEach player rolls one die. (one cube)
UseEach player rolls two dice. (two cubes)
AvoidEach player rolls one dice. (if you mean one cube)
Dictionaries now also list dice as a singular. However, many people still consider this use an error, and they judge the speaker who uses dice for one cube.