Correct spelling, explanation: oldest and eldest are not interchangeable. While both words convey the idea of being the oldest in some context, they have specific and distinct uses. Confusion often arises because people may not be aware of the specific usage of eldest within family dynamics and may use oldest instead, especially when speaking casually or informally. To avoid confusion, it’s helpful to be aware of the correct usage of each word and apply them accordingly, especially when discussing family members or siblings.

Definition of eldest:
adjective, being the oldest of three or more people, especially within a family
The eldest son in the family inherited the responsibility of taking care of the family business.
As the eldest sibling, she often acted as a role model and mentor to her younger brothers and sisters.

Collocations with :
Some most commonly used collocations include:
1. Eldest child: refers to the firstborn or oldest child in a family.
The eldest child often bears the responsibility of setting an example for their younger siblings.
2. Eldest son/daughter: specifically describes the oldest male or female child in a family.
The eldest son inherited his father’s estate when he passed away.
3. Eldest sibling: refers to the oldest brother or sister in a family.
The eldest sibling in their family always took charge during family gatherings.

Correct spelling, explanation: the words oldest and eldest share the same root, which is the Old English word ēald, meaning old. Over time, English developed different forms to express the idea of being the oldest or most senior, and oldest and eldest are the modern derivatives of this common root. Both words ultimately trace their origins back to the same source but have evolved to serve slightly different grammatical and contextual purposes in contemporary English. Remember that oldest and eldest don’t mean the same thing.