siren: a sea nymph (part woman and part bird) supposed to lure sailors to destruction on the rocks where the nymphs lived
sea nymph: (Greek mythology) a water nymph who was the daughter of Oceanus or Nereus
myasthenia gravis: a chronic progressive disease characterized by chronic fatigue and muscular weakness (especially in the face and neck); caused by a deficiency of acetylcholine at the neuromuscular junctions