Meaning : An earnest and sincere feeling.
Synonyms : earnestness, sincerity
Meaning : The quality of arousing fear or distress.
Example :
He learned the seriousness of his illness.
Synonyms : distressfulness
Meaning : The trait of being serious.
Example :
A lack of solemnity is not necessarily a lack of seriousness.
Synonyms : earnestness, serious-mindedness, sincerity