From the experts:
Osian is the easier-to-comprehend version of the ancient Irish Oisin, an important name in mythology. Osian or Oisin was a warrior poet. Osian is popular in modern Wales and England. While Oisin is pronounce oh-SHEEN, Osian is pronounced o-SHAN -- though we bet most Americans would just say ocean, which you may consider a good thing.