​FOOL’S PARSLEY, in botany, the popular name for Aethusa Cynapium, a member of the family Umbelliferae, and a common weed in cultivated ground. It is an annual herb, with a fusiform root and a smooth hollow branched stem 1 to 2 ft. high, with much divided (ternately pinnate) smooth leaves and small compound umbels of small irregular white flowers. The plant has a nauseous smell, and, like other members of the order (e.g. hemlock, water-dropwort), is poisonous.