The difference between Serious and Unimportant

When used as adjectives, serious means without humor or expression of happiness, whereas unimportant means petty.

check bellow for the other definitions of Serious and Unimportant

Serious as an adjective:

Without humor or expression of happiness; grave in manner or disposition

Examples:

"It was a surprise to see the captain, who had always seemed so serious, laugh so heartily."

"synonyms: earnest solemn"
Serious as an adjective:

Important; weighty; not insignificant

Examples:

"This is a serious problem. We'll need our best experts."
Serious as an adjective:

Really intending what is said; in earnest; not jocular or deceiving

Examples:

"After all these years, we're finally getting serious attention."