Difference between Firstborn and Eldest

Firstborn

Part of speech: adjective

Definition: Born as the first one in a family, flock or the like. Most excellent; most distinguished or exalted.

Part of speech: noun

Definition: The first child to be born to a parent or family.

Eldest

Part of speech: adjective

Definition: Most old; greatest in age or seniority.

Example sentence: Self-defence is Nature's eldest law.