From Longman Dictionary of Contemporary Englishjackbootjack‧boot /ˈdʒækbuːt/ noun [countable] DCCa boot worn by soldiers that covers their leg up to the knee —jackbooted adjective
Examples from the Corpus
jackboot• A jackboot serial killer on the loose, stomping down the humanist softies of soul?• Expressionless, their ill-fitting jackboots thumping up and down as they marched, the soldiers approached the lone kilted figure.• One can not support Fulani, whether by vote or contribution, without aiding the jackboot movement behind her.• They will feel the jackboot upon their necks.• The Guardia Nacional wear jackboots and hook their fingers in their trigger guards.Origin jackboot (1600-1700) Perhaps from jack “soldier's coat” ((14-19 centuries)) (from French jaque; → JACKET) + boot 