skull and crossbonesnoun [ S ]
uk/ˌskʌl ən ˈkrɒs.bəʊnz/us/ˌskʌl ən ˈkrɑːs.boʊnz/a picture of a skull with two long bones crossing each other under it that warns of death or danger, used in the past on pirate flags and now on containers or places containing dangerous substances or machinery