‘Elder’ refers to someone who is older than you in your family or sibling group. For example, ‘My elder brother is a lawyer.’. On the other hand, ‘eldest’ is used to refer to the oldest person in a group of siblings. For instance, ‘My eldest sister is a doctor.’. More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.