One of the popular synonyms for the word "death-heads" is "skull and bones." This term refers to the use of a skull and crossbones as a symbol of danger or death. Another synonym for "death-heads" is "Grim Reaper," which is a common personification of death in folklore and mythology. "Black flag" is also a synonym for "death-heads," as it refers to a symbolic flag that pirates used to fly when they were about to attack or plunder a ship. Lastly, "memento mori" is a synonym for "death-heads," which is a Latin phrase that means "remember that you will die," often used to urge people to reflect on the brevity of life.