Possibly feminine form of Orestes, from Greek 'oros' meaning 'mountain'; a rare poetic name.
Oressa may be a feminine form of Orestes, tied to Greek roots meaning mountain. That gives the name a subtle classical and geographic strength beneath its softer surface. It sounds poetic and uncommon. Oressa has a quiet grandeur, the kind of rare name that feels both learned and airy, with just enough mythological connection to give it depth.