skull and crossbones /ˌskʌlənˈkrɑːsˌboʊnz/ noun /ˌskʌlənˈkrɑːsˌboʊnz/
noun
Learner's definition of SKULL AND CROSSBONES
[singular]
: a picture of a human skull above two crossed bones that was used on the flags of pirate ships in the past and is now used as a warning label on containers of poisonous or dangerous substances骷偻画(过去用在海盗船旗上,现在作为危险标志用在装有毒物品或危险品的容器上)