1. Gravity of manner or mind; earnest attention, particularly to religious concerns.

Nuttall's Standard dictionary of the English language By Nuttall, P.Austin

• seriousiness,
• serioiusness,
• seriousnous,
• seriosness,
• seriouslness,
• seriuosness,
• seriusnes,
• seriousniss,
• serousness,
• seriouseness,
• seriusness,
• seriouness,
• seriousnes,
• serouisness,
• furiousness,
• feriousness,
• -perilousness,
• perrilousness,
• perillousness,
• unmericfulness

• serious music.

The adjective form of the word "seriousness" is "serious".

The plural of the "seriousness" can be the "seriousnesses".

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