General relationships:
* Collateral: This word emphasizes a relationship stemming from a common ancestor, but not directly in line of descent.
* Lateral: This term signifies a relationship that's parallel or to the side, often used in organizational structures.
* Adjacent: This word implies being physically or conceptually next to something else.
* Peripheral: This term suggests a relationship that's on the edge or less central.
Specific contexts:
* Sibling: For family relationships, this term denotes a brother or sister.
* Cousin: This term describes a relative through a parent's brother or sister.
* Neighbor: For geographic relationships, this signifies someone who lives nearby.
* Allied: This term applies to political or military relationships where entities are on the same side.
Other options:
* Contiguous: This word indicates things being physically or conceptually next to each other.
* Side by side: This phrase describes a relationship where two things are situated next to each other.
* Parallel: This term describes a relationship where two things run alongside each other.
To choose the best word, consider the specific context and the relationship you're trying to describe.