'Memento mori' definitions:

Definition of 'memento mori'

(from WordNet)
noun
A reminder (as a death's head) of your mortality

Definition of 'Memento mori'

From: GCIDE
  • Memento mori \Me*men"to mo"ri\ [L.] Lit., remember to die, i.e., that you must die; a warning to be prepared for death; an object, as a death's-head or a personal ornament, usually emblematic, used as a reminder of death. [Webster 1913 Suppl.]