Half-share is a term used to describe when two individuals share equal ownership or responsibility for something. There are several synonyms that can be used to express the same concept, including joint ownership, co-ownership, shared responsibility, partnership, and collaboration. Joint ownership and co-ownership both emphasize the aspect of sharing ownership, whereas shared responsibility and partnership place more emphasis on the shared responsibility aspect. Collaboration, on the other hand, is often used in the context of working together towards a common goal or project. These synonyms for half-share can be used interchangeably depending on the specific context and the desired connotations or emphasis.