anticholinesterase: a medicine that inhibits cholinesterase by combining with it and so has a cholinergic effect
medicine: (medicine) something that treats or prevents or alleviates the symptoms of disease
tropic: either of two parallels of latitude about 23.5 degrees to the north and south of the equator representing the points farthest north and south at which the sun can shine directly overhead and constituting the boundaries of the Torrid Zone or tropics