The word "stheno" comes from Greek mythology and refers to one of the three Gorgons. The Gorgons are mythical creatures that are often depicted as having snakes for hair and the ability to turn people to stone with their gaze. Stheno is specifically known as one of the two immortal Gorgons, alongside her sister Euryale, while the third Gorgon, Medusa, is mortal.
Understanding "stheno" requires knowledge of Greek mythology, specifically the Gorgons.