(US, military, slang) a member of the United States Marine Corps
Word Origin
C20: so called because of their distinctive haircut
Word Origin and History for jarhead
n.
"U.S. Marine," by 1985 (but in a biographical book with a World War II setting), from jar + head. Also used as a general term of insult (by 1979) and by 1922 as a Georgia dialectal word for "mule."