From leather + neck.
leatherneck (plural leathernecks)
- (slang) A soldier.
- (US) Specifically, a marine.
- 2011, Steven Pinker, The Better Angels of Our Nature, Penguin 2012, p. 318:
- The Marine Corps has instituted a martial-arts program in which leathernecks are indoctrinated in a new code of honor, the Ethical Marine Warrior.