Erymanthis, in the tale of Heracles' Fourth Labour, was the name of the mountain in Arcadia where the Erymanthian Boar lived. This mountain was said to have taken its name from a son of Apollo who had been blinded by Aphrodite because he had seen her bathing naked (compare the fate of Actaeon).
The name seems to be based on mantice, 'divination' with the suffix ery- coming from eryo, 'to draw'. It thus means 'divining by lots', which is presumably intended as a powerful and propitious name.