monkshood

noun

1. a plant belonging to the genus Aconitum, of the buttercup family, especially A. napellus, the flowers of which have a large, hood-shaped sepal.

noun

1. any of several poisonous N temperate plants of the ranunculaceous genus Aconitum, esp A. napellus, that have hooded blue-purple flowers

n.also monk’s-hood, 1570s, from monk (n.) + hood (n.1). So called for the shape of the flowers.