Pronunciation: (sēr'ē-us), [key]
1. of, showing, or characterized by deep thought.
2. of grave or somber disposition, character, or manner: a serious occasion; a serious man.
3. being in earnest; sincere; not trifling: His interest was serious.
4. requiring thought, concentration, or application: serious reading; a serious task.
5. weighty or important: a serious book; Marriage is a serious matter.
6. giving cause for apprehension; critical: The plan has one serious flaw.
7. Med.(of a patient's condition) having unstable or otherwise abnormal vital signs and other unfavorable indicators, as loss of appetite and poor mobility: patient is acutely ill.
that which is of importance, grave, critical, or somber: You have to learn to separate the serious from the frivolous.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.