They briefly called it 'Eclipse'.

Yes, after they found out Medicine Head had already used ‘Dark Side of the Moon’, they switched to ‘Eclipse’ for a while.

Medicine Head released an album called Dark Side of the Moon in 1972, so Pink Floyd changed their working title to Eclipse — which is the name of the closing track on the eventual album. But Medicine Head’s album tanked, so Floyd’s label convinced them it was safe to go back to The Dark Side of the Moon. They did.

Good thing they changed it back. Eclipse works as a track title but not as an album name for what became one of the biggest records ever.