serious (Adjective) — Concerned with work or important matters rather than play or trivialities. ex. "a serious student of history" ex. "a serious attempt to learn to ski" ex. "gave me a serious look" ex. "a serious young man" ex. "are you serious or joking?" ex. "Don't be so serious!"
serious (Adjective) — Of great consequence. ex. "marriage is a serious matter"
serious (Adjective) — Causing fear or anxiety by threatening great harm. ex. "a serious wound"
serious (Adjective) — Appealing to the mind. ex. "a serious book"
serious (Adjective) — Completely lacking in playfulness.
serious (Adjective) — Requiring effort or concentration; complex and not easy to answer or solve. ex. "raised serious objections to the proposal" ex. "the plan has a serious flaw"