Aconitum napellus aco·ni·tum·napellus uncommon noun 1. a poisonous herb native to northern Europe having hooded blue-purple flowers; the dried leaves and roots yield aconite Synonymsmonkshoodhelmetflowerhelmet flowerAconitum napellus Related words Broader terms aconite WordNet 2.1 (Princeton University). WordNet 2.1 Copyright Princeton University. All rights reserved.