the mind > mental capacity > memory > reminder, putting in mind > [noun] > as injunction or warning > object > reminding of death (2)
A warning or reminder of the inevitability of death, esp. a skull or other symbolic object. Later sometimes in weakened use: any grim, ominous, or…
A representation of a human skull, as an emblem or reminder of death or mortality. Also skull and crossbones, a representation of a bare skull…