seriousness

n. 严肃, 认真

The reader who do not detect the seriousness under the lightness often misread him.

没有意识到轻松掩盖下的严肃性的读者常常会误解他。

If I could intrude a note of seriousness into this frivolous conversation...

我真想说一句, 叫他们谈话放严肃些....