IPA: /ˈfɜrstˌbɔrn/
KK: /ˈfɜrstˌbɔrn/
The term refers to the child who is born first in a family.
As the firstborn, she often felt responsible for her younger siblings.
The first child born to a family.
She is the firstborn in her family and has two younger siblings.
Firstborn → It is formed from "first" (from Old English "fyrst", meaning earliest or prior) and "born" (from Old English "boren", meaning to be born). The word "firstborn" refers to the first child born to a parent.
Think of the word 'first' meaning earliest and 'born' meaning to come into the world — that's why firstborn refers to the first child born.
No commonly confused words.