Co Ownership, Joint Ownership, Share
noun, verbal noun, の adjective
The things you together have are the things that are shared.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
"That is a very nice yacht. Is that yours, Mr. Tanaka?" "I'm a co-owner with my brother."
These One Piece figures are the shared assets of Koichi and Viet.
Raising a kid works better when husbands and wives share information properly.