ice vs hoarfrost

ice and hoarfrost both are nouns.

Word	Noun	Adjective	Verb	Adverb
ice	Yes	No	Yes	No
hoarfrost	Yes	No	No	No

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

ice: water frozen in the solid state
hoarfrost: ice crystals forming a white deposit (especially on objects outside)

Other hyponyms of ice include black ice, frost, hoar, rime, hailstone, icicle, ground ice, segregated ice, Taber ice.

ice (noun)	hoarfrost (noun)
a rink with a floor of ice for ice hockey or ice skating	ice crystals forming a white deposit (especially on objects outside)
an amphetamine derivative (trade name Methedrine) used in the form of a crystalline hydrochloride; used as a stimulant to the nervous system and as an appetite suppressant
a frozen dessert with fruit flavoring (especially one containing no milk)
a flavored sugar topping used to coat and decorate cakes
the frozen part of a body of water
diamonds
water frozen in the solid state