IPA: /ˈaɪsiər/
KK: /ˈaɪsiər/
More cold and covered with ice than something else.
The weather today is icier than it was yesterday.
Comparative: icier
Superlative: iciest
Icier is formed from "ice" (from Old English "is", meaning frozen water) and the suffix "-ier" (a comparative suffix indicating more of a quality). The word "icier" means having more ice or being more cold than something else.
Think of 'ice' as the base, and remember that 'icier' means more like ice or colder.