ichthyology - the branch of zoology that studies fishes

icily - ADj in an icy manner: I received him icily because of the harsh way he had treated me.

ideology - an orientation that characterizes the thinking of a group or nation

Idiom -an expression whose meaning is not predictable from the usual meanings of its constituent elements, as kick the bucket or hang one's head, or from the general grammatical rules of a language, as the table round for the round table, and that is not a constituent of a larger expression of like characteristics.

idiosyncrasy - a behavioral attribute that is distinctive and peculiar to an individual