A light, close-fitting helmet or skull-cap worn in medieval times, often made of steel and covering only the top and back of the head.
From Old French cervellière, from cervelle (brain), because the helmet protected the brain area; the spelling reflects French etymology even in English, similar to how we borrowed 'chandelier' from French.
Medieval knights wore these lightweight brain-protecting helmets when they wanted mobility over maximum protection—so calling something a 'cerveliere' literally meant 'brain-keeper,' which is adorably direct for a piece of armor.
Complete word intelligence in one call. Free tier — 50 lookups/day.