This sentence is in a cambridge dictionary;
A sibling is a brother or sister. Sibling rivalry means rivalry between children in a family.
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A sibling is a brother or sister. Sibling rivalry means rivalry between children in a family.
Sibling rivalry is a common issue for parents. The first born child will be an only child until the second is born. It is normal for the first born to be jealous of the younger sibling.
You can read about it here: https://kidshealth.org/en/parents/sibling-rivalry.html