serious

adjective

1. concerned with work or important matters rather than play or trivialities"a serious student of history"
2. of great consequence"marriage is a serious matter"
3. causing fear or anxiety by threatening great harm"a dangerous operation"
4. appealing to the mind"good music"
5. completely lacking in playfulness
6. requiring effort or concentration; complex and not easy to answer or solve"raised serious objections to the proposal"