Half-sibling
A sibling sharing only one parent — kin through one side of the family but not the other.
A half-sibling in a dream is the dream's image of kin shared through one parent but not the other. The relationship is real, and the relationship is also asymmetric; one history is shared, one is not. The dream brings the half-sibling when an alliance in your life — a colleague who shares one of your formative experiences but not the others, a friend who knows you from one period only — is operating on partial common ground. A half-sibling encountered warmly is the dream telling you the partial kinship is enough for what is being asked of it. A half-sibling encountered with tension is the dream noting that the shared half is being claimed for more than it can carry, and the unshared half is being denied.