I.e. "the powerful," or " the strengthening."
1. A surname of Zeus, under which he had an altar in a rock near Hermione, where Aegeus concealed his sword and his shoes, which were found there by Theseus after he had lifted up the rock. (Paus. ii. 32. § 7, 34. § 6.)
2. One of the horses of Poseidon also bore the Sthenius. (Schol. ad Hom. Il. xiii. 23.)