English

jarhead

From jar + head, due to the regulation high and tight haircut of the Marines.

A compound of jar + head

Middle English jarre

English jar

Proto-Indo-European *kap- ‘head’

…

Proto-Germanic *haubudą ‘head’

Proto-West Germanic *haubud

Old English hēafod ‘head’

Middle English heed ‘head’

English head

Today it means

noun A US marine.

Language periods are conventional ranges, not dates for this word.