jack ‧ boot /ˈdʒækbuːt/ BrE AmE noun [countable]
[ Date: 1600-1700 ; Origin: Perhaps from jack 'soldier's coat' (14-19 centuries) (from French jaque ; ⇨ ↑ jacket ) + boot ]
a boot worn by soldiers that covers their leg up to the knee
—jackbooted adjective