Terran German jackboots from 1914 CE.
A hobnail.
A jackboot is a military boot such as the cavalry jackboot or the hobnailed jackboot. The cavalry jackboot was a version of the jackboots worn by postilions, such as guided the French stage coach.
The hobnailed jackboot has a different design and function than the first type. It is a combat boot that is designed for marching. It rises to mid-calf or higher with no laces and usually has a leather sole with hobnails.
These boots have both been associated with totalitarianism, as they were worn by the Nazis and were used by armies in the former Soviet Union.
The word is commonly used in Britain as a synonym for fascism. The Russian expression "под сапогом" "under one's boot" translates as "under one's heel" and symbolizes oppression. The Spanish expression "tener (algo o alguien) bajo la bota" or "to have (something or somebody) under the boot" has the same meaning.