• fristborn,
• firstborned,
• dirstborn,
• cirstborn,
• virstborn,
• girstborn,
• tirstborn,
• rirstborn,
• furstborn,
• fjrstborn,
• fkrstborn,
• forstborn,
• fierstborn,
• frstborn,
• firsborn,
• firtsborn,
• firstbron,
• firrstborn,
• firstbornn,
• fyrstborn

• first step,
• firestone,
• firestorm,
• first state,
• first-rater,
• firsthand,
• first-year,
• first-rate,
• first moment,
• firstly,
• firestine,
• first cousin,
• first grade,
• First Reich,
• first name,
• first floor,
• first gear,
• first-string.

The adjective form of "firstborn" is "firstborn".

The plural of the "firstborn" can be the "firstborn".

The singular of the "firstborn" can be the "firstborn".