Something that’s icky is disgusting and gummy or sticky. When you walk around a busy city all day, you’re bound to end up with something icky stuck to the bottom of your shoe.
After frolicking through the mud, your dog with be dirty and icky, and a particularly humid summer day can feel icky too. You can also use icky to simply mean “yucky” or “nasty,” as when your school cafeteria offers several icky dishes for lunch, like mystery meat and mystery mash. The informal icky is an American invention, from the 1920’s slang icky-boo, baby talk for “sick” or “nauseated.”