Definition of jarhead in English:

jarhead

Pronunciation /ˈjärˌhed/ /ˈdʒɑrˌhɛd/

noun

informal US
  • A US Marine.

    • ‘After all, how could some jarhead Marine know more about any subject than the Washington Post?’
    • ‘The entire manner in which the heavily criticized Patriot Act was passed into law is enough to give even the most jingoistic jarhead reason to pause.’

Origin

Early 20th century (originally US dialect, in the sense ‘mule’): from jar+ head. The word originally referred to members of the US army, on account of the mule mascot of the Army football teams.