apartener
The term "apartener" is not a recognized word in standard English dictionaries or common parlance. It appears to be a portmanteau, a blending of two or more words. The most likely components are "apartment" and "partner."
If interpreted as "apartment partner," it would refer to an individual with whom one shares living quarters
Alternatively, "apartener" could potentially be a misspelling or a neologism with a less common meaning. Without