firstborn; first child; eldest child
Refers to the first child born to a parent or couple. Neutral term used in family contexts, medical records, and official forms.
She just gave birth to her first child.
When their first child was born, the husband was overjoyed.
一人っ子 means an only child, not necessarily the firstborn; 第一子 implies there may be younger siblings.
Standard kanji spelling using 第一 (first) + 子 (child).
Variant with numeral 1; common in forms and official documents.
Compound of 第一 (first) + 子 (child). The reading だいいっし follows the standard on'yomi with a geminate consonant (促音) between いち and し.