Serious

adjective
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.
Medicine/Medical. (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.
noun
8.
that which is of importance, grave, critical, or somber:
You have to learn to separate the serious from the frivolous.
adjective
1.
grave in nature or disposition; thoughtful: a serious person
2.
marked by deep feeling; in earnest; sincere: is he serious or joking?
3.
concerned with important matters: a serious conversation
4.
requiring effort or concentration: a serious book
5.
giving rise to fear or anxiety; critical: a serious illness
6.
(informal) worthy of regard because of substantial quantity or quality: serious money, serious wine
7.
(informal) extreme or remarkable: a serious haircut

serious se·ri·ous (sēr’ē-əs)
adj.
Being of such import as to cause anxiety, as of a physical condition.
serious