Returning to where it began. Of a shape with no end, or a reasoning that assumes what it set out to show.

Having a way it points. Direction adds an asymmetry that position alone does not have.

The prefix of again — return, repetition, renewal; meaning's way of coming back.

To put one thing where another was. Replacement fills the role and is not the same thing.

To turn about a centre. Also to replace in turn — the same word for spinning and for taking turns.