"Backness" is a term used to describe a position or state that is situated at the rear or behind something or someone. However, if you are seeking alternative words to communicate the same idea, here are a few synonyms to consider. "Rearward" emphasizes the direction towards the back. "Posterior" describes something situated at the rear or bottom. "Hindmost" refers to the furthest position towards the back. "Reversed" suggests a backward or opposite orientation. "Retrospective" denotes a focus on past events or looking back. These synonyms can be used interchangeably with "backness" to convey the desired meaning with a slightly different flavor or connotation.