crossbones

Crossbones is a symbol consisting of two long bones crossed at their centers, typically forming an X shape. The phrase is often used together with a skull in the familiar "skull and crossbones" motif, but crossbones can be depicted without a skull. The bones are usually depicted as femurs or tibias, but any long bones may be used in symbolic renderings.

Historically, crossbones appear in heraldry and funerary art as a sign of mortality and warning. In medieval and early modern Europe, the motif appeared on coats of arms and on coffins and tombs as memento mori. The modern association with piracy comes from the Jolly Roger flags of the early 18th century; though the exact origins are unclear, crossbones became a common emblem of piracy by the mid-1700s.

In contemporary use, crossbones are widely recognized as a warning symbol for poison and hazardous substances. In labeling, it typically appears with a skull to indicate danger. The symbol also appears in heraldic contexts, graphic design, fashion, and popular culture, where it connotes danger, rebellion, or nautical piracy. Variants include different bone types, orientations, and the omission of the skull.