oposaka → oɸosaka → owosaka → oosaka → oːsaka. Compound of 大(ō, “great”) and 阪(saka, “hill”). The geographical area was historically known as 小坂(Osaka, Ozaka, “little hill”) and was renamed to Ōsaka / Ōzaka "great hill". Originally spelled as 大坂 before being replaced with 大阪.