Skull and crossbones, a symbol of death. See Crossbones.
Skull"cap` (?), n. 1. A cap which fits the head closely; also,
formerly, a headpiece of iron sewed inside of a cap for protection.
2. (Bot.) Any plant of the labiate genus Scutellaria, the calyx of
whose flower appears, when inverted, like a helmet with the visor
raised.