Icky is informal, especially American, for something very unpleasant — often sticky, slimy, too sweet, dirty, or just ugly to look at, taste, or touch. A child might say a vegetable is icky, or that a slug feels icky. Adults use it too, but it sounds playful or childish, not like a word for a serious school essay. It appeared in American English in the 1930s, from earlier baby-talk icky-boo, meaning sickly or about to feel sick — a child’s soft twist on sick. It was also used, a little sentimentally, for a kind of jazz. There is no “ice” hiding in this word, and it is not the same as icy (cold, or unfriendly).