dice vs D4

dice and D4 both are nouns.

Word	Noun	Adjective	Verb	Adverb
dice	Yes	No	Yes	No
D4	Yes	No	No	No

As nouns, D4 is a hyponym of dice; that is, D4 is a word with a more specific, narrower meaning than dice:

dice: a small cube with 1 to 6 spots on the six faces; used in gambling to generate random numbers
D4: a four-sided die

Other hyponyms of dice include five-spot, five, four-spot, four, one-spot, six-spot, six.

dice (noun)	D4 (noun)
a small cube with 1 to 6 spots on the six faces; used in gambling to generate random numbers	a four-sided die

dice (verb)	D4 (verb)
play dice
cut into cubes