water ice vs icicle

water ice and icicle both are nouns.

Word	Noun	Adjective	Verb	Adverb
water ice	Yes	No	No	No
icicle	Yes	No	No	No

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

water ice: water frozen in the solid state
icicle: ice resembling a pendent spear, formed by the freezing of dripping water

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

water ice (noun)	icicle (noun)
an ice containing no milk but having a mushy consistency; usually made from fruit juice	ice resembling a pendent spear, formed by the freezing of dripping water
water frozen in the solid state